Button-hole (A).
A flower inserted in the button-hole of a coat.
“In fine wéather he [the driver of a hansom] will sport a button-hole—generally a dahlia, or some flower of that ilk.”—Nineteenth Century (March, 1893, p. 473).
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Entry taken from Dictionary of Phrase and Fable, edited by the Rev. E. Cobham Brewer, LL.D. and revised in 1895.