Piano's part in works of Tchaikovsky (4)
I believe the answer is:
soft
'piano's' is the definition.
('soft' can be similar in meaning to 'piano')
'part in works of tchaikovsky' is the wordplay.
'part in' says the answer is hidden in the clue.
'SOFT' is hidden in the letters of 'works of tchaikovsky'.
(Other definitions for soft that I've seen before include "Lenient; not coarse" , "Cushy, not tough" , "Mild" , "Pliant" , "Not hard, rough or harsh" .)