A narrow bed, usually one of two stacked vertically in a small space; also slang for nonsense or a false excuse.
Possibly from Swedish 'bänk' (bench) or Scandinavian languages. The 'nonsense' meaning may be short for 'bunk' as in worthless or empty talk, from a different root meaning 'to dodge' or 'avoid.'
It's funny that the same word means both a sleeping bed and 'nonsense'—this happened because sailors used 'bunk' for ship beds, and then 'bunk' also came to mean dodging duty, so 'bunk' became synonymous with avoiding or dismissing something.
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