E. Cobham Brewer 1810–1897. Dictionary of Phrase and Fable. 1898.
Nightcap (A).
A glass of grog before going to bed. Supposed to promote sleep.
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“The nightcap is generally a little whisky left in the decanter. To do it honour it is taken neat. Then all get up and wish ‘good-night.’”—Max O’Rell: Friend MacDonald, iii.
