Member steps under the bar briefly? (4)
I believe the answer is:
limb
'member' is the definition.
(member can mean a limb)
'steps under the bar briefly?' is the wordplay.
'steps under the bar' becomes 'limbo' (dance steps done under a bar).
'briefly?' means to remove the last letter (I've seen 'briefly' mean this).
'limbo' with its final letter taken off is 'LIMB'.
(Other definitions for limb that I've seen before include "Large tree branch" , "arm, perhaps" , "Bough" , "Branch - member" , "Human's extension" .)