Large portion of chicken or moussaka (8)
I believe the answer is:
enormous
'large' is the definition.
(similar in meaning)
'portion of chicken or moussaka' is the wordplay.
'portion of' indicates the answer is hidden within the clue.
'ENORMOUS' is hidden within 'chicken or moussaka'.
(Other definitions for enormous that I've seen before include "Colossal, huge" , "Fat" , "Huge, tremendous" , "Unusually large - jumbo" , "Gross" .)