Member returned in fat dancer's costume (7)
I believe the answer is:
leotard
'dancer's costume' is the definition.
'member returned in fat' is the wordplay.
'member' becomes 'toe' (toe is a kind of member).
'returned' shows that the letters should be reversed in order.
'in' means one lot of letters goes inside another.
'fat' becomes 'lard' (lard is a kind of fat).
'toe' written backwards gives 'eot'.
'eot' put within 'lard' is 'LEOTARD'.
(Other definitions for leotard that I've seen before include "Stretchy one-piece garment" , "One-piece garment worn by acrobat" , "Dancers might wear this" , "Dancer's tight-fitting garment" , "Do alter for acrobat's garment" .)