piano vs pianissimo

piano and pianissimo both are nouns.

Word	Noun	Adjective	Verb	Adverb
piano	Yes	Yes	No	Yes
pianissimo	Yes	Yes	No	Yes

As nouns, piano and pianissimo are synonyms defined as:

piano (noun)	pianissimo (noun)
a keyboard instrument that is played by depressing keys that cause hammers to strike tuned strings and produce sounds	(music) low loudness
(music) low loudness

piano (adjective)	pianissimo (adjective)
(used chiefly as a direction or description in music) soft; in a quiet, subdued tone	(chiefly a direction or description in music) very soft

piano (adverb)	pianissimo (adverb)
used as a direction in music; to be played relatively softly	a direction in music; to be played very softly