Fat member back in dancewear (7)
I believe the answer is:
leotard
'dancewear' is the definition.
(I know that leotard is a type of dancewear)
'fat member back in' is the wordplay.
'fat' becomes 'lard' (lard is a kind of fat).
'member' becomes 'toe' (toe is a kind of member).
'back' says the letters should be written in reverse.
'in' means one lot of letters goes inside another.
'toe' back-to-front is 'eot'.
'lard' going around 'eot' is 'LEOTARD'.
(Other definitions for leotard that I've seen before include "Ballet outfit" , "Skin-tight garment worn by acrobats" , "Dance/exercise garment" , "Garment worn by ballet dancers" , "Stretchy one-piece garment" .)