ticket collector vs doorkeeper

ticket collector and doorkeeper both are nouns.

Word	Noun	Adjective	Verb	Adverb
ticket collector	Yes	No	No	No
doorkeeper	Yes	No	No	No

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

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

Other hypernyms of ticket collector include door guard, doorman, gatekeeper, hall porter, ostiary, porter.

ticket collector (noun)	doorkeeper (noun)
someone who is paid to admit only those who have purchased tickets	someone who guards an entrance
	an official stationed at the entrance of a courtroom or legislative chamber
	the lowest of the minor Holy Orders in the unreformed Western Church but now suppressed by the Roman Catholic Church