"optical instrument which by means of a lens or lenses magnifies and renders visible minute objects or details of visible bodies," 1650s, from Modern Latin microscopium, literally "an instrument for viewing what is small;" see micro- + -scope. The dim southern constellation Microscopium was among those introduced by La Caille in 1752.
1650s, "hair splitting, exaggerated attention to petty things," from Latinized form of Greek mikrologia "pettiness, care for trifles," from mikros (see micro-) + -logia (see -logy). By 1849 as "the part of science devoted to microscopic investigation," a separate coinage from microscope. Related: Micrological.
early 15c., "an opening, hole, orifice," from Latin apertura "an opening," from apertus, past participle of aperire "to open, uncover," from PIE compound *ap-wer-yo- from *ap- "off, away" (see apo-) + root *wer- (4) "to cover." In optics, diameter of the exposed part of a telescope, microscope, etc., 1660s.
late 14c., magnifien, "to speak or act for the glory or honor (of someone or something)," from Old French magnefiier "glorify, magnify," from Latin magnificare "esteem greatly, extol, make much of," from magnificus "great, elevated, noble," literally "doing great deeds," from magnus "great" (from PIE root *meg- "great") + combining form of facere "to make, to do" (from PIE root *dhe- "to set, put").
Meaning "increase the apparent size of by use of a telescope or microscope" is from 1660s, said to be a development peculiar to English. Related: Magnified; magnifying. Magnifying glass is by 1650s.