A person who complains frequently and persistently about things, often in an annoying way.
From 'bellyache' (to complain) plus the agent suffix '-er' (one who does something). This American slang term emerged in the early 20th century to describe a habitual complainer.
Bellyacher is pure American slang ingenuity—by the 1920s-30s, it became the insult of choice for annoying whiners, appearing frequently in film noir dialogue and detective stories.
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