insecticide is a modern coinage from insect (from Latin insectum 'cut into segments', from insecare 'to cut into', from in- + secare 'to cut') + -cide (from Latin caedere 'to kill'). Morphologically, the ending is part of the etymology: the suffix is attached to the older base named in the history, producing a later English derivative. In present English, the noun sense is "a substance used to kill insects", so the historical development ends in a clearly identifiable modern dictionary use. The same base also appears in related forms such as insect, insectivore, homicide, and pesticide, and in derivatives such as insecticidal. Its semantic neighborhood includes pesticide and bug spray, which helps locate the modern sense without adding a separate etymological claim. The named historical forms include Latin insectum and Latin caedere.