Bathrobe serving to conceal fat? (5)
I believe the answer is:
obese
'fat?' is the definition.
('obese' can be similar in meaning to 'fat')
'bathrobe serving to conceal' is the wordplay.
'to conceal' indicates the answer is hidden within the clue.
'OBESE' is hidden in the letters of 'bathrobe serving'.
(Other definitions for obese that I've seen before include "round" , "More than podgy" , "Excessively fat" , "Very substantial" , "Roly-poly" .)