E. Cobham Brewer 1810–1897. Dictionary of Phrase and Fable. 1898.
Putting on Side.
Giving oneself airs. Side is an archaic word for a train or trailing gown; also long, as “his beard was side.” A side-coat means a long trailing coat. (Anglo-Saxon sid, great, wide, long—as sid-feax, long hair.)
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“I do not like side frocks for little girls.”—Skinner.
