prison guard vs gaoler

prison guard and gaoler both are nouns.

Word	Noun	Adjective	Verb	Adverb
prison guard	Yes	No	No	No
gaoler	Yes	No	No	No

As nouns, prison guard and gaoler are synonyms defined as:

Other synonyms of prison guard include jailer, jailor, screw, turnkey.

prison guard (noun)	gaoler (noun)
someone who guards prisoners	someone who guards prisoners