Fat Romeo grabbed by groom (4)
I believe the answer is:
lard
'fat' is the definition.
(I know that lard is a type of edible fat)
'romeo grabbed by groom' is the wordplay.
'romeo' becomes 'r' (phonetic alphabet: alpha, bravo, charlie etc.).
'grabbed by' indicates putting letters inside (inserted letters are grabbed inside).
'groom' becomes 'lad' (I've seen this in another clue).
'r' put within 'lad' is 'LARD'.
(Other definitions for lard that I've seen before include "White cooking fat" , "Animal fat" , "Aggrandise - embellish" , "Fat Scottish landowner appears disheartened" , "Pig fat used in cooking" .)