nightcap

The word 'nightcap' is a transparent compound formed from two native English roots, 'night' and 'cap'. Its primary literal sense, dating to the 14th century, was a simple cloth covering worn on the head for warmth while sleeping. The more figurative sense, an alcoholic drink taken at bedtime, emerged in the early 19th century. This semantic extension was driven by the conceptual link between the comforting function of the physical cap and the soothing, sleep-inducing effect of the final drink of the evening, effectively 'capping off' the night.

Structure: night (time of darkness) + cap (head covering) - night: From Old English niht, of Germanic origin; related to Dutch nacht and German Nacht, from an Indo-European root shared by Latin nox and Greek nux. Functions as a noun root specifying a time period. - cap: From Old English cæppe, from Late Latin cappa "hood, cloak". Functions as a noun root denoting a type of head covering.