Old English hassuc "clump of grass, coarse grass," of unknown origin. Sense of "thick cushion" is first recorded 1510s, with the likely connection being the perceived similarity of a kneeling cushion and a tuft of grass. Related: Hassocky.
"to feed on grass," Old English grasian, from græs "grass" (see grass). Compare Middle Dutch, Middle High German grasen, Dutch grazen, German grasen. Transitive sense from 1560s. Figurative use by 1570s. Related: Grazed; grazing.
"long grass, second growth of grass after mowing," late 14c., probably of Scandinavian origin; compare Norwegian fogg "long grass in a moist hollow," Icelandic fuki "rotten sea grass." A connection to fog (n.1) via a notion of long grass growing in moist dells of northern Europe is tempting but not proven. Watkins suggests derivation from PIE *pu- (2) "to rot, decay" (see foul (adj.)).
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.