crabgrass (n.)

also crab-grass, 1590s, from crab (n.1) + grass. Originally a marine grass of salt marshes (Salicornia herbacea) perhaps so called because it was supposed to be eaten by crabs; modern use, in reference to Panicum sanguinale, an annual grass cultivated on waste land (but a noxious weed in lawns and cultivated fields), is from 1743, perhaps partly in reference to its crooked form.