very softly vs pianissimo

very softly is not a noun while pianissimo is a noun.

Word	Noun	Adjective	Verb	Adverb
very softly	No	No	No	Yes
pianissimo	Yes	Yes	No	Yes

As adverbs, very softly and pianissimo are synonyms defined as:

very softly and pianissimo: a direction in music; to be played very softly

very softly (noun)	pianissimo (noun)
	(music) low loudness

very softly (adjective)	pianissimo (adjective)
	(chiefly a direction or description in music) very soft

very softly (adverb)	pianissimo (adverb)
a direction in music; to be played very softly	a direction in music; to be played very softly