pestis + -cīda

Pesticide is a modern coinage from Latin pestis (plague, pestilence, destructive thing) and -cīda (killer), from caedere (to cut, to kill). The word appeared in English around 1939, when the first modern synthetic pesticides were being developed. DDT, synthesized by Paul Hermann Müller in 1939, was the compound that made the word necessary — for the first time, a single chemical product could kill a wide range of insect pests, and language needed a word for the category.

DDT won Müller the Nobel Prize in Physiology or Medicine in 1948. It had saved millions of lives by killing malaria-carrying mosquitoes in wartime military campaigns. The word pesticide carried positive connotations in the 1940s and 1950s — it named humanity's ability to control nature. DDT was sprayed from trucks through American neighborhoods while children played in the mist. The word suggested progress.

Rachel Carson's Silent Spring, published in 1962, reversed the word's connotation. Carson documented how DDT accumulated in food chains, thinning the eggshells of birds of prey and threatening entire species with extinction. The book is widely credited with launching the modern environmental movement. The word pesticide, after Carson, carried a warning. The plague-killer could become a plague itself.

The United States banned DDT in 1972. The word pesticide now names a global industry worth over $65 billion annually. Pesticides include insecticides, herbicides, fungicides, rodenticides, and dozens of subcategories. The word is a political battleground: organic advocates oppose pesticides; conventional farmers depend on them; regulators negotiate between them. The Latin word for plague created a word that is itself controversial in every language.