Etymology is the study of the origins and development of words. By extension, it’s sometimes used to refer to the origins of a word. Entomology is the study of insects. If it helps, think of the word as antomology, but with an e instead of an a.
Examples
“Indian summer” is of American etymology and best describes the US climate. [Irish Times]
Baylor has entomology classes for studying insects. [Baylor Lariat]
The etymology of the Glaswegian word “bevvy” is not difficult to unravel. [The Guardian]
Lately, the entomologist has been noticing the pests everywhere—even on the small species of elm growing in front of a Columbia coffee shop. [Baltimore Sun]