In science, vacuist, as opposed to a “plenist” (or Aristotelian), refers to one who believes in the existence of the vacuum; both are pre 18th century (1701-1800) terms.

The following are related quotes:

“These and many other considerations are adduced on both sides of this question. Melchior Cornaeus (ΡΊ), professor of theology at our own university of Wurzburg, has learned and at some length argued these matters in a discussion of his own dedicated to this topic. On several occasions he and I observed and carefully scrutinized the experiments in question. When I first saw them, I sent an account to Kircher at Rome and to some other friends and scholars, asking their opinion of them. All of them sided with the Aristotelians against the ‘vacuists’. Among the replies I received was [a Feb 1656] letter from Kircher.”
Gaspar Schott (c.1656), summary of communications on Otto Guericke’s vacuum experiments [1]

See also
● Vacuum break
● Vacuum bulb
● Vacuum pump

1. (a) Schott, Gaspar. (1657). Mechanica hydraulico-pneumatica (§:Experimentum Novum Magdeburgicum, pgs. 441-88; Vacuist, pgs. 451-52). Publisher.
(b) Conlon, Thomas. (2011). Thinking About Nothing: Otto von Guericke and the Magdeburg Experiments on the Vacuum (vacuist, pgs. 67, 319). Saint Austin Press/LuLu.

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