Jack's portion of jellied eels (3)
I believe the answer is:
dee
'jack's' is the definition.
(Jack Dee is a comedian)
'portion of jellied eels' is the wordplay.
'portion of' says the answer is hidden in the clue.
'DEE' is hidden in the letters of 'jellied eels'.
(Other definitions for dee that I've seen before include "Name of many rivers" , "Aberdeen's river" , "River of Scotland" , "Aberdeenshire river" , "River name" .)