The lowest part of a ship's interior where water collects; also means nonsense or foolish talk.
Possibly from Old French 'bille' (tree trunk or log), or from a Dutch/Flemish origin. The nautical sense came first—the lowest point in a ship's hull where dirty water gathers, then metaphorically extended to mean 'garbage' or 'worthless talk.'
The fact that sailors used 'bilge' for both literal dirty water in the ship's lowest point AND for ridiculous talk shows how perfectly the word captured the gross nature of both—bilge is basically the sewage of language!
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