Butcher's tip to get ace kind of fillet (4)
I believe the answer is:
bone
'kind of fillet' is the definition.
(fillet on the bone)
'butcher's tip to get ace' is the wordplay.
'tip' indicates taking the first letters (I've seen 'tips' mean this (tip can refer to the top end of something)).
'to get' means one lot of letters go next to another.
'ace' becomes 'one' (synonyms).
The first letter of 'butchers' is 'b'.
'b'+'one'='BONE'
(Other definitions for bone that I've seen before include "Ossified material" , "See 6" , "Skeleton component" , "Skeletal segment" , "Eg, radius or stirrup" .)