Webster's Revised Unabridged Dictionary · 1913

Bleat

Bleat ({not transcribed}) , intransitive verb

[Old English bleten, Anglo-Saxon blatan; akin to Dutch blaten, bleeten, Old High German blāzan, plāzan; prob. of imitative origin.]

To make the noise of, or one like that of, a sheep; to cry like a sheep or calf.
Then suddenly was heard along the main, To low the ox, to bleat the woolly train. — Pope
The ewe that will not hear her lamb when it baas, will never answer a calf when he bleats. — Shakespeare

Bleat , noun

A plaintive cry of, or like that of, a sheep.
The bleat of fleecy sheep. — Chapman's Homer