doorman vs door guard

doorman and door guard both are nouns.

Word	Noun	Adjective	Verb	Adverb
doorman	Yes	No	No	No
door guard	Yes	No	No	No

As nouns, doorman and door guard are synonyms defined as:

Other synonyms of doorman include doorkeeper, gatekeeper, hall porter, ostiary, porter.

doorman (noun)	door guard (noun)
someone who guards an entrance	someone who guards an entrance