oat

Short definition from Wiktionary

Noun

1. 1
   Widely cultivated cereal grass, typically Avena sativa.
2. 2
   Any of the numerous species, varieties, or cultivars of any of several similar grain plants in genus Avena.
3. 3
   The seeds of the oat, a grain, harvested as a food crop and for animal feed.
4. 4
   A simple musical pipe made of oat-straw.
5. 5
   The tiniest amount; a whit or jot.

Prepositional phrase

1. 1
   Alternative letter-case form of OAT.
2. 2
   Initialism of of all time.