signaller vs ringer

signaller and ringer both are nouns.

Word	Noun	Adjective	Verb	Adverb
signaller	Yes	No	No	No
ringer	Yes	No	No	No

As nouns, ringer is a hyponym of signaller; that is, ringer is a word with a more specific, narrower meaning than signaller:

Other hyponyms of signaller include signalman, bell ringer, toller, whistler.

signaller (noun)	ringer (noun)
someone who communicates by signals	(horseshoes) the successful throw of a horseshoe or quoit so as to encircle a stake or peg
	a contestant entered in a competition under false pretenses
	a person who is almost identical to another
	a person who rings church bells (as for summoning the congregation)