To make the characteristic crying sound of a goat or sheep; to cry or complain in a whining voice.
From Old English 'blætan,' possibly imitative of the actual sound a goat makes. The onomatopoeia is ancient, showing how long humans have heard and described this animal sound.
Calling someone's complaint a 'bleat' is clever insult language—it compares human whining to a goat's cry, which is why sheep characters in literature often seem foolish, as if the sound itself is inherently annoying to human ears.
Complete word intelligence in one call. Free tier — 50 lookups/day.