Proper gravy with roast, finally (4)
I believe the answer is:
just
'proper' is the definition.
(thesaurus)
'gravy with roast finally' is the wordplay.
'gravy' becomes 'jus' (jus is a type of gravy).
'with' says to put letters next to each other.
'finally' suggests the final letters.
The final letter of 'roast' is 't'.
'jus'+'t'='JUST'
(Other definitions for just that I've seen before include "Book by Richmal Crompton" , "Fair - precisely" , "Barely; impartial" , "And nothing more" , "Simply - fair" .)