Only gravy on last of meat (4)
I believe the answer is:
just
'only' is the definition.
(synonyms)
'gravy on last of meat' is the wordplay.
'gravy' becomes 'jus' (jus is a type of gravy).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'last of' says to take the final letters.
The final letter of 'meat' is 't'.
'jus'+'t'='JUST'
(Other definitions for just that I've seen before include "Exactly" , "Fair and proper" , "Merited" , "Book by Richmal Crompton" , "Simply - fair" .)