zoo keeper vs steward

zoo keeper and steward both are nouns.

Word	Noun	Adjective	Verb	Adverb
zoo keeper	Yes	No	No	No
steward	Yes	No	No	No

As nouns, steward is a hypernym of zoo keeper; that is, steward is a word with a broader meaning than zoo keeper:

Other hypernyms of zoo keeper include custodian, keeper.

zoo keeper (noun)	steward (noun)
the chief person responsible for a zoological garden	someone who manages property or other affairs for someone else
	a union member who is elected to represent fellow workers in negotiating with management
	one having charge of buildings or grounds or animals
	an attendant on an airplane
	the ship's officer who is in charge of provisions and dining arrangements