water boy vs assistant

water boy and assistant both are nouns.

Word	Noun	Adjective	Verb	Adverb
water boy	Yes	No	No	No
assistant	Yes	Yes	No	No

As nouns, assistant is a hypernym of water boy; that is, assistant is a word with a broader meaning than water boy:

water boy: an assistant who supplies drinking water
assistant: a person who contributes to the fulfillment of a need or furtherance of an effort or purpose

Other hypernyms of water boy include help, helper, supporter.

water boy (noun)	assistant (noun)
an assistant who supplies drinking water	a person who contributes to the fulfillment of a need or furtherance of an effort or purpose

water boy (adjective)	assistant (adjective)
	of or relating to a person who is subordinate to another