Hordeum hor·deum uncommon noun 1. annual to perennial grasses of temperate northern hemisphere and South America: barley Synonymsgenus Hordeum Related words Word family Hordeum jubatumHordeum murinumHordeum pusillumHordeum vulgare Broader terms monocot genus Parts Gramineae Part of barley WordNet 2.1 (Princeton University). WordNet 2.1 Copyright Princeton University. All rights reserved.