to utter the characteristic deep sound of a cow; low.
noun, plural moos.
2.
a mooing sound.
Origin
1540-50; imitative
British Dictionary definitions for moo
moo
/muː/
verb
1.
(intransitive) (of a cow, bull, etc) to make a characteristic deep long sound; low
interjection
2.
an instance or imitation of this sound
Word Origin and History for moo
v.
"to make the characteristic sound of a cow," 1540s, of imitative origin. Related: Mooed; mooing. The noun is from 1789. Baby-talk moo-cow (n.) attested from 1812.