Make fun of nudes dancing on piano (4,2)
I believe the answer is:
'make fun of' is the definition.
(I've seen this before)
'nudes dancing on piano' is the wordplay.
'dancing' is an anagram indicator.
'on' says to put letters next to each other.
'piano' becomes 'p' (musical abbreviation).
'nudes' anagrammed gives 'sendu'.
(Other definitions for send up that I've seen before include "Make fun of or despatch aloft" , "Mock?" , "Satirise" , "Mockery" , "Parody (of something)" .)