Silly space cadet undressed in prank (8)
I believe the answer is:
escapade
'prank' is the definition.
(I've seen this before)
'silly space cadet undressed' is the wordplay.
'silly' is an anagram indicator.
'undressed' indicates the central letters (the word removes the letters which clothe it).
The centre of 'cadet' is 'ade'.
'space' with letters rearranged gives 'escap'.
'escap'+'ade'='ESCAPADE'
'in' acts as a link.
(Other definitions for escapade that I've seen before include "Mischievous romp" , "Wild and exciting undertakings" , "Antic" , "Wild prank" , "Adventurous T [TREAT]" .)