sofa vs convertible

sofa and convertible both are nouns.

Word	Noun	Adjective	Verb	Adverb
sofa	Yes	No	No	No
convertible	Yes	Yes	No	No

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

Other hyponyms of sofa include sofa bed, daybed, divan bed, divan, love seat, loveseat, tete-a-tete, vis-a-vis, settee, squab.

sofa (noun)	convertible (noun)
an upholstered seat for more than one person	a car that has top that can be folded or removed
	a sofa that can be converted into a bed
	a corporate security (usually bonds or preferred stock) that can be exchanged for another form of security (usually common stock)

sofa (adjective)	convertible (adjective)
	capable of being exchanged for or replaced by something of equal value
	designed to be changed from one use or form to another
	capable of being changed in substance as if by alchemy