entomologist n.

"the branch of zoology which treats of insects," 1764, from French entomologie (1764), coined from -logie "study of" (see -logy) + Greek entomon "insect," neuter of entomos "cut in pieces, cut up," in this case "having a notch or cut (at the waist)," from en "in" (see en- (2)) + temnein "to cut" (from PIE root *tem- "to cut").

Insects were so called by Aristotle in reference to the segmented division of their bodies. Compare insect, which is from a Latin loan-translation of the Greek word. Related: Entomological; entomologically. Hybrid insectology (1766, from French insectologie, 1744) is not much used.

I have given the name insectology to that part of natural history which has insects for its object; that of entomology ... would undoubtedly have been more suitable ... but its barbarous sound terryfy'd me. [Charles Bonnet's English translation of his "Contemplation de la nature," 1766]

word-forming element meaning "one who does or makes," also used to indicate adherence to a certain doctrine or custom, from French -iste and directly from Latin -ista (source also of Spanish, Portuguese, Italian -ista), from Greek agent-noun ending -istes, which is from -is-, ending of the stem of verbs in -izein, + agential suffix -tes.

Variant -ister (as in chorister, barrister) is from Old French -istre, on false analogy of ministre. Variant -ista is from Spanish, popularized in American English 1970s by names of Latin-American revolutionary movements.