Christmas box vs pourboire

Christmas box and pourboire both are nouns.

Word	Noun	Adjective	Verb	Adverb
Christmas box	Yes	No	No	No
pourboire	Yes	No	No	No

As nouns, pourboire is a hypernym of Christmas box; that is, pourboire is a word with a broader meaning than Christmas box:

Christmas box: a present given at Christmas for services during the year
pourboire: a relatively small amount of money given for services rendered (as by a waiter)

Other hypernyms of Christmas box include backsheesh, baksheesh, bakshis, bakshish, gratuity, tip.

Christmas box (noun)	pourboire (noun)
a present given at Christmas for services during the year	a relatively small amount of money given for services rendered (as by a waiter)