The word "entomology" entered English in 1766 from French entomologie, coined from Greek entomon (insect) and -logia (study of, discourse about). The Greek word entomon is the neuter form of entomos (cut into, notched), from the verb entemnein (to cut into), combining en- (in) with temnein (to cut). Aristotle used entomon to describe insects because their bodies appear to be cut into distinct segments — head, thorax, and abdomen separated by visible constrictions.
The descriptive logic of the Greek name parallels the Latin-derived word "insect" exactly. Latin insectum (cut into) is a calque — a literal translation — of Greek entomon. Both words describe the same observable feature: the segmented body plan that distinguishes insects from other arthropods. Pliny the Elder explicitly noted this when he introduced insectum as the Latin equivalent
Greek temnein (to cut) generated several other English words. "Atom" comes from atomos (uncuttable, indivisible), "anatomy" from anatemnein (to cut up, to dissect), "tome" from tomos (a section, a cutting — hence a volume of a multi-volume work), and "epitome" from epitemnein (to cut short, to abridge). All these words preserve the cutting metaphor: atoms are what cannot be cut further, anatomy is the art of cutting apart, and a tome is a cut section of a larger work.
The notorious confusion between "entomology" and "etymology" provides endless amusement for practitioners of both fields. The two words differ by a single letter, and their pronunciation is nearly identical. Etymologists routinely receive emails about beetle identification, while entomologists are asked about word origins. The confusion is especially ironic because both Greek roots
Entomology became a formal scientific discipline in the 18th century, though the study of insects is far older. Aristotle classified insects in his Historia Animalium, and Chinese silk production depended on detailed knowledge of the silkworm's life cycle for millennia. Modern entomology encompasses an enormous field: there are more known insect species (over one million) than all other animal species combined, and estimates suggest that millions more remain undescribed.