Look adopted by gentleman with trendy cut (7)
I believe the answer is:
sirloin
'cut' is the definition.
(I know that sirloin is a type of cut of beef)
'look adopted by gentleman with trendy' is the wordplay.
'look' becomes 'lo' ('lo' is an archaic exclamation meaning 'look!').
'adopted by' is an insertion indicator (I've seen this in other clues).
'gentleman' becomes 'sir' (a man may be addressed as sir).
'with' is a charade indicator (letters next to each other).
'trendy' becomes 'in' ('in' can mean fashionable).
'sir'+'in'='sirin'
'lo' placed into 'sirin' is 'SIRLOIN'.
(Other definitions for sirloin that I've seen before include "Choice cut of beef" , "(Knighted?) cut of meat" , "Joint of beef" , "Prime cut of beef" , "Quality cut of beef loin" .)