perquisite vs gratuity

perquisite and gratuity both are nouns.

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

As nouns, gratuity is a hyponym of perquisite; that is, gratuity is a word with a more specific, narrower meaning than perquisite:

perquisite: an incidental benefit awarded for certain types of employment (especially if it is regarded as a right)
gratuity: a relatively small amount of money given for services rendered (as by a waiter)

Other hyponyms of perquisite include apanage, appanage, backsheesh, baksheesh, bakshis, bakshish, pourboire, tip.

perquisite (noun)	gratuity (noun)
a right reserved exclusively by a particular person or group (especially a hereditary or official right)	a relatively small amount of money given for services rendered (as by a waiter)
an incidental benefit awarded for certain types of employment (especially if it is regarded as a right)	an award (as for meritorious service) given without claim or obligation