Paraquat Trade name for an organic herbicide used to control broadleaved weeds and grasses (see viologen dyes). It is poisonous to humans, having toxic effects on the liver, lungs, and kidneys if ingested. Paraquat is not easily broken down and can persist in the environment adsorbed to soil particles. See also pesticide.

par·a·quat / ˈparəˌkwät/ • n. a toxic, fast-acting herbicide that becomes deactivated in the soil.

Paraquat (pa-ră-kwot) n. Trademark. the chemical compound dimethyl dipyridilium, widely used as a weed-killer. When swallowed it exerts its most serious effects upon the lungs, the tissues of which it destroys after a few days.