1.nounA warm cloth cap worn while sleeping, often with pajamas, being common attire in northern Europe before effective home heating became widespread.
"Winston wore a nightcap to stave off the cold."
2.nounA beverage drunk before bed that is usually alcoholic.
"I'll make myself a nightcap of whisky and lemon before heading to bed."
3.noun(by extension) Something the person reads or listens to before bed.
4.nounThe final match of a sporting contest, especially the second game of a baseball doubleheader.
5.nounA cap drawn over the face of the condemned person before they are hanged.