blue devils

Originally apparitions supposed to be seen by sufferers of delirium tremens.

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blue devils pl (plural only)

1. (slang, idiomatic) Low spirits; depression.
   • 1890, William Morris, News from Nowhere, in the journal The Commonweal. (First published in book form 1890.)

     "[…] the disease is either extinct, or exists in such a mild form that a short course of aperient medicine carries it off. It is sometimes called the Blue-devils now or the Mulleygrubs. Queer names, ain't they?"

2. (slang, figuratively) Depressants, especially the barbiturate amobarbital.

• (depression): mulligrubs