Definition of "oat"

oat

/əʊt/

noun
countable and uncountable, plural oats
1. (uncountable) Widely cultivated cereal grass, typically Avena sativa.
2. (countable) Any of the numerous species, varieties, or cultivars of any of several similar grain plants in genus Avena.
3. (usually as plural) The seeds of the oat, a grain, harvested as a food crop.
  Quotations
  The point is, except in Scotland, people eat comparatively few oats. Scotland's another story, though you'll have to decide how seriously to take it. The way the story goes is that in eastern Scotland, the unmarried plowmen didn't eat anything but oats and milk, except for an occasional potato.
  1991, Cornelia M. Parkinson, Cooking with Oats: Oat Bran, Oatmeal, and More, Storey Publishing, page 2
4. A simple musical pipe made of oat-straw.
5. The tiniest amount; a whit or jot.
  Quotations
  Few of them care an oat for the niceties of the arrow sport, but for the young lords that may be on a hunt!
  1994, Susan King, The Black Thorne's Rose, page 21