Ron used to cook steak (9)
I believe the answer is:
tournedos
'steak' is the definition.
(I know that tournedos is a type of fillet)
'ron used to cook' is the wordplay.
'cook' indicates anagramming the letters.
'ron'+'used'+'to'='ronusedto'
'ronusedto' is an anagram of 'TOURNEDOS'.
(Other definitions for tournedos that I've seen before include "Round thick piece of beef fillet" , "Steaks" , "Thick slice" , "Small round thick beef fillet" , "Steak" .)