To be seen displaying fat? (5)
I believe the answer is:
obese
'fat?' is the definition.
('obese' can be similar in meaning to 'fat')
'to be seen displaying' is the wordplay.
'displaying' says the answer is hidden in the clue.
'OBESE' can be found hidden inside 'to be seen'.
(Other definitions for obese that I've seen before include "likely to tip the balance?" , "Much too fat" , "porky?" , "Stout" , "Unhealthily large" .)