foghorn vs diaphone

foghorn and diaphone both are nouns.

Word	Noun	Adjective	Verb	Adverb
foghorn	Yes	No	No	No
diaphone	Yes	No	No	No

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

foghorn: a warning device consisting of a horn that generates a loud low tone
diaphone: a foghorn that makes a signal consisting of two tones

foghorn (noun)	diaphone (noun)
a warning device consisting of a horn that generates a loud low tone	a foghorn that makes a signal consisting of two tones
a loud low warning signal that can be heard by fogbound ships