hautboy vs heckelphone

hautboy and heckelphone both are nouns.

Word	Noun	Adjective	Verb	Adverb
hautboy	Yes	No	No	No
heckelphone	Yes	No	No	No

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

hautboy: a slender double-reed instrument; a woodwind with a conical bore and a double-reed mouthpiece
heckelphone: an oboe pitched an octave below the ordinary oboe

Other hyponyms of hautboy include basset oboe, musette pipe, oboe da caccia, oboe d'amore, shawm.

hautboy (noun)	heckelphone (noun)
a slender double-reed instrument; a woodwind with a conical bore and a double-reed mouthpiece	an oboe pitched an octave below the ordinary oboe