lengthiness vs fermata

lengthiness and fermata both are nouns.

Word	Noun	Adjective	Verb	Adverb
lengthiness	Yes	No	No	No
fermata	Yes	No	No	No

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

lengthiness: the consequence of being lengthened in duration
fermata: (music) a prolongation of unspecified length on a note or chord or rest

lengthiness (noun)	fermata (noun)
amount or degree or range to which something extends	(music) a prolongation of unspecified length on a note or chord or rest
the consequence of being lengthened in duration	a musical notation (over a note or chord or rest) that indicates it is to be prolonged by an unspecified amount