"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]
It is the hypothetical source of/evidence for its existence is provided by: Greek temnein "to cut," tomos "volume, section of a book," originally "a section, piece cut off;" Old Church Slavonic tina "to cleave, split;" Middle Irish tamnaim "I cut off," Welsh tam "morsel."