ticket taker vs gatekeeper

ticket taker and gatekeeper both are nouns.

Word	Noun	Adjective	Verb	Adverb
ticket taker	Yes	No	No	No
gatekeeper	Yes	No	No	No

As nouns, gatekeeper is a hypernym of ticket taker; that is, gatekeeper is a word with a broader meaning than ticket taker:

ticket taker: someone who is paid to admit only those who have purchased tickets
gatekeeper: someone who guards an entrance

Other hypernyms of ticket taker include door guard, doorkeeper, doorman, hall porter, ostiary, porter.

ticket taker (noun)	gatekeeper (noun)
someone who is paid to admit only those who have purchased tickets	someone who guards an entrance
	someone who controls access to something