Insecticide joins insect to -cide, a killing ending. Insect itself comes from Latin insectum, a form of the participle insectus, from insecare, to cut into. Its components are in- and secare. The older animal name evokes the notched appearance of a segmented body.
Sources
- Merriam-Webster: insecticide
The headword is International Scientific Vocabulary and names a substance used to kill insects.
- Merriam-Webster: insect
Insectum is the neuter of insectus, participle of insecare, to cut into, from in- and secare; the essay relates the name to the notched appearance of a segmented body.
- Merriam-Webster: in-
The relevant Latin prefix derives from in, in or into; it is separate from the negative prefix.
- Merriam-Webster: -cide
The English ending means killer or killing and traces through French to Latin killing formations.
- Collins: insecticide
The formation is insect with -cide, including a connecting -i- in one analysis.
- Online Etymology Dictionary: -cide
Also built on *-cide* "killer": herbicide, fungicide
- Online Etymology Dictionary · insecticide
Meanings of the older forms on the word path.