Tickle the ivories: you perform sonata, finally, when retired (5)
I believe the answer is:
amuse
'tickle' is the definition.
(I've seen this before)
'the ivories you perform sonata finally when retired' is the wordplay.
'finally' indicates one should take the final letters.
'when retired' says the letters should be written in reverse.
The last letters of 'the ivories you perform sonata' are 'esuma'.
'esuma' backwards is 'AMUSE'.
(Other definitions for amuse that I've seen before include "Keep someone entertained" , "Pleasantly occupy" , "Delight" , "Divert or entertain mildly" , "Cause mirth - distract" .)