clover (n.) Look up clover at Dictionary.com
Old English clafre, from Proto-Germanic *klaibron (cf. Middle Low German klever, Middle Dutch claver, Dutch klaver, Old Saxon kle, Old High German kleo, German Klee "clover"), of uncertain origin.

Liberman suggests it is probably from West Germanic *klaiwaz- "sticky pap" (see clay), and adds, "The sticky juice of clover was the base of the most popular sort of honey." First reference in English to the suposed luck of a four-leaf clover is from c.1500. To be in clover "live luxuriously" is 1710, "clover being extremely delicious and fattening to cattle" [Johnson].