Insect lived on piano (4)
I believe the answer is:
wasp
'insect' is the definition.
(I know that wasp is a type of insect)
'lived on piano' is the wordplay.
'lived' becomes 'was' ('be' can be a synonym of 'live').
'on' says to put letters next to each other (in a down clue, letters appear on others).
'piano' becomes 'p' (musical abbreviation).
'was'+'p'='WASP'
(Other definitions for wasp that I've seen before include "Striped insect" , "Insect often irritating in summer" , "Social worker" , "Buzzer" , "A hymenopteran" .)