gratuity vs pourboire

gratuity and pourboire both are nouns.

Word	Noun	Adjective	Verb	Adverb
gratuity	Yes	No	No	No
pourboire	Yes	No	No	No

As nouns, gratuity and pourboire are synonyms defined as:

gratuity and pourboire: a relatively small amount of money given for services rendered (as by a waiter)

Other synonyms of gratuity include backsheesh, baksheesh, bakshis, bakshish, tip.

gratuity (noun)	pourboire (noun)
a relatively small amount of money given for services rendered (as by a waiter)	a relatively small amount of money given for services rendered (as by a waiter)
an award (as for meritorious service) given without claim or obligation