means A chemical substance used to kill or control pests — insects, weeds, fungi, rodents, and other unwanted organisms.

from A modern compound stitched from the Latin 'pestis,' meaning plague or pestilence, and the suffix '-cide,' from Latin 'caedere,' to cut down or kill — the same '-cide' that ends 'homicide' and 'genocide.' So at root the word literally means 'plague-killer,' a 20th-century coinage that rose with industrial agriculture and the synthetic chemistry boom.