oat

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of various grasses of the genus Avena, especially A. sativa, widely cultivated for their edible grains.
• noun The grain of any of these plants, used as food and fodder.
• noun A musical pipe made of an oat straw.

from The Century Dictionary.

• noun A cereal plant, Avena sativa, or its seed: commonly used in the plural in a collective sense.
• noun Any species of Avena. The wild oat of Europe, A. fatua, is a weed of cultivation in many places; in California, where it abounds, it is extensively utilized as hay. The animal, fly, or hygrometric oat, A. sterilis, native in Barbary, has two long, strong, much-bent awns, which twist and untwist with changes of moisture, and so become a means of locomotion. Various species are more or less available for pasture.
• noun A musical pipe of oat-straw; a shepherd's pipe; hence, pastoral song. See oaten pipe, under oaten.
• noun Bromus secalinus.
• noun Pharus latifolius.
• To feed with oats; feed oats to.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Bot.) A well-known cereal grass (Avena sativa), and its edible grain, used as food and fodder; -- commonly used in the plural and in a collective sense.
• noun obsolete A musical pipe made of oat straw.
• noun (Bot.) A grass (Avena sterilis) much like oats, but with a long spirally twisted awn which coils and uncoils with changes of moisture, and thus gives the grains an apparently automatic motion.
• noun (Zoöl.), [Prov. Eng.] the snow bunting; -- so called from its feeding on oats.
• noun (Bot.) the name of several grasses more or less resembling oats, as Danthonia spicata, Danthonia sericea, and Arrhenatherum avenaceum, all common in parts of the United States.
• noun [Slang] to feel lively and energetic.
• noun to indulge in youthful dissipation.
• noun (Bot.) a grass (Avena fatua) much resembling oats, and by some persons supposed to be the original of cultivated oats.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun uncountable Widely cultivated cereal grass, typically Avena sativa.
• noun countable Any of the numerous species, varieties, or cultivars of any of several similar grain plants.
• noun usually as plural The seeds of the oat, harvested as a food crop.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun seed of the annual grass Avena sativa (spoken of primarily in the plural as `oats')
• noun annual grass of Europe and North Africa; grains used as food and fodder (referred to primarily in the plural: `oats')