Definition of oat
1a
: any of several grasses (genus Avena)
especially
: a widely cultivated cereal grass (A. sativa)
b
: a crop or plot of the oat
also
: the seed of an oat
—usually used in plural but singular or plural in construction
2
archaic
: a reed instrument made of an oat straw
feel one's oats
: to act in a newly self-confident and often self-important manner
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Merriam-Webster unabridged
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Time Traveler for oat
The first known use of oat was before the 12th century
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