|The general "underlying" meaning of the circa 1920s introduced term "biophysics", a conjunction of "bio-" + "-physics", short for "physical biology" (1915), i.e. the physical chemistry of zoology and botany, generally meant to mean the study of the physics and chemistry and or physical chemistry of organisms (plants and animals), internally and or evolving systems, but anchored in the term "life" (or living matter) or "bio-" which has its definitional roots in ancient religion (i.e. god created "plant life" on the third day, "animal life" on the fifth day, and "human life", via clay creation myth, on the sixth day) and mythology (Greek mythology, in particular, per "bio-" origin), both preceded by Anunian theology (3100BC), and older folklore before that.|
Etymology | Physical biology → Biophysics
In 1915, German engineer-mathematician Walter Porstmann (1886-1959), in his “A problem from the Physical Zoology: influence of Physical Moments on the Shape of the Fish”, argued for the need for a new science of physical zoology and botany, along the lines of physical chemistry; his main statement on this is as follows: 
“It will be the function of this new branch of science to investigate biological phenomena as regards their physical aspects, just as ‘physical chemistry’ has treated the physical aspects of chemical phenomena. Because this field has not yet been systematically explored the individual data of ‘physical biology’ appear, as yet, as more or less disconnected facts, or as regularities for which no proper place is found in the existing scheme of present-day science; and the investigations of isolated problems in this field are as yet carried on as something of a scientific hobby by amateurs, with the result that they are guided by chance rather than by plan, and are often totally lacking in any fundamental guiding principles or connecting theory. As results gathered in this disconnected fashion accumulate, the need of their unification into a harmonious whole, into a distinct discipline of science, becomes more and more acutely felt. Such unification necessarily involves the working out of a viewpoint that shall make the several facts and relations fall in line naturally in an orderly system; in other words, what is needed is a labor of organization. In the course of this, new and unforeseen problems will inevitably arise, and a fruitful field of scientific endeavor should thus be opened for the investigator.”
In 1920, American electrophysiologist Alexander Forbes (1882-1965) (Ѻ), in his Science article “Biophysics”, according to Lotka (1925), outlined “what might be termed the program of biophysics”.  This seems to be the first "coined" usage of the term "biophysics".
In 1921, Irish physiological chemist David Burns published his An Introduction to Biophysics, which was a basic physiology textbook of sorts. 
In Jan 1922, Alfred Lotka wrote a letter to Raymond Pearl wherein he vents on Burns' An Introduction to Biophysics, as a semi-contender to his own line of research, in the previous two-decades, albeit a physiology (physics inside the organism) book, thereby differing from Lotka’s “nature as one gigantic whole” model: 
“The time is ripe. I see many signs of the fact. Have you seen a recently published book by Burns and Paton, An Introduction to Biophysics? It also dug a spur into my side—not that there is anything to get excited over, the book would hardly be described as either inspired or inspiring. But it shows the undercurrent, which one of the days must break through to the surface.”
Sharon Kingsland (1995) suggests that “these currents” carried Lotka into a decision in 1922 to accept a fellowship at Johns Hopkins, wherein he would spend the next two years writing Elements of Physical Biology, completed in 1924 and published in 1925, wherein he differentiates between the terms biophysics (physics inside the organism) and physical biology (physics of systems of organisms).
In 1925, Alfred Lotka, in his §5:Program of Physical Biology”, citing Forbes and Porstmann, gave the following bold type definition:
“Physical biology, as here conceived and discussed, is essentially a branch of the greater discipline of the ‘general mechanics of evolution, the mechanics of systems undergoing irreversible changes in the distribution of matter among the several components of such system. In introducing the term ‘physical biology’ the writer would suggest that the term ‘biophysics’ be employed (as hitherto) to denote that branch of science which treats of the physics of individual life processes, as exhibited in the individual organism (e.g., conduction of an impulse along nerve or muscle); and that the term ‘physical biology’ be reserved to denote the broader field of the application of physical principles in the study of life-bearing systems as a whole. Physical biology would, in this terminology, include biophysics as a subordinate province.”
This definition, of significant note, was preceded by his ripe §1:Regarding Definitions, wherein he goes into persuasive argument about how there are issues with the attempts to define “life”, i.e. the “bio-”, according to physicochemical principles, but that he does not know presently how to resolve the issue, and thereby retains the term “life”, and related, for practical purposes.
In 1950, John Butler, together with J.T. Randall, in their Progress in Biophysics and Biophysical Chemistry, the first of an annual journal of sorts, opened to the following synopsis or journal aim: (Ѻ)
“While there is general agreement that biophysics is a very important and rapidly developing branch of science, it is a little difficult at present to decide precisely what should be its scope, and the editors of this volume, which is the first of a new series, have recognised the difficulty by including biophysical chemistry as well as biophysics in the title. The book itself consists of nine articles by authorities on particular topics, which vary widely in scope from a highly specialised discussion of "Local Refractometry" by Philpot to a four-page summary of "Phase-contrast Microscopy in Biological Research" by Hughes. Readers of a chemical turn of mind will particularly welcome Gutfreund's article on the "Properties of solutions of Large Molecules", Rudall's article on "Fundamental Structures in Biological System" and Crane's on "Bioelectric Potentials, their Maintenance and Function". Those who are more physically inclined will turn to Oster's review of the "Scatterig of Visible Light and X-rays by Solutions of Proteins", and Engstrom's on the "Use of soft X-rays in the Assay of Biological Materials", while physiologists will be particularly attracted by Pryor's discussion of the "Mechanical Properties of Fibres and Muscles" and Loutit's review of "The Tolerance of Man for Radioactive Isotopes". The book forms a useful addition to the now formidable and still rapidly expanding array of reviews and annuals, since it covers that land between the physical and the biological sciences which most reviews have until recently avoided. The editors are to be congratulated on the wide choice of material for this first volume of what should prove to be a very useful series. J. N. Davidson.”
Bio | Note
The prefix “bio-”, in short, is a defunct term (see: defunct theory of life; life does not exist); the upgrade prefix substitute for “bio” presently is “powered CHNOPS+ matter” (or powered CHNOPS+# phase) (see: life terminology upgrades), e.g. Henry Adams (1908) defined himself as a "powered CHNOPS+20 phase" (see: social phase), so to speak, in modern exact mass composition terminology, and Wilhelm Ostwald (1926) defined himself as a "C-H-N-O-S-P combination"; a windmill or a robot, e.g., are types of animate matter, but one would not classify these as having the same “physics” properties as say a butterfly or a grass growing.
1. (a) Kurzynski, Michal. (2006). The Thermodynamic Machinery of Life. New York: Springer.
(b) Physics – EtymOnline.com.
2. (a) Porstmann, Walter. (1915). “A problem from the Physical Zoology: influence of Physical Moments on the Shape of the Fish” (“Ein Problem aus der physikalischer Zoologie: Einfluss hysikalischer Momente auf die Gestalt der Fische”), Prometheus, 26:267-70; 284-86; 300-303.
(b) Walter Portsmann (German → English) – Wikipedia.
(c) Lotka, Alfred J. (1925). Elements of Physical Biology (republished (Ѻ) as: Elements of Mathematical Biology, which includes: corrections from Lotka’s notes and a completed list of his publications) (pdf) (Ѻ) (txt) (Porstmann, pg. 45). Dover, 1956.
(d) Kingsland, Sharon E. (1995). Modelling Nature: Episodes in the History of Population Ecology (Ostwald, pg. 35). University of Chicago Press.
3. (a) Forbes, Alexander. (1920). “Biophysics”, Science, 52:331-32.
(b) Lotka, Alfred J. (1925). Elements of Physical Biology (republished (Ѻ) as: Elements of Mathematical Biology, which includes: corrections from Lotka’s notes and a completed list of his publications) (pdf) (Ѻ) (txt) (Porstmann, pg. 45). Dover, 1956.
4. Lotka, Alfred J. (1925). Elements of Physical Biology (republished (Ѻ) as: Elements of Mathematical Biology, which includes: corrections from Lotka’s notes and a completed list of his publications) (pdf) (Ѻ) (txt) (Porstmann, pg. 45). Dover, 1956.
5. Burns, David. (1921). An Introduction to Biophysics. J. & A. Churchill.
6. (a) Lotka, Alfred. (1922). “Letter to Pearl”, Jan 31; Pearl Papers.
(b) Kingsland, Sharon E. (1995). Modelling Nature: Episodes in the History of Population Ecology (Pearl, pg. 32; Ostwald, pg. 35). University of Chicago Press.
● Biophysics – Wikipedia.