Knight to look fashionable with cut (7)
I believe the answer is:
sirloin
'cut' is the definition.
(I know that sirloin is a type of cut)
'knight to look fashionable' is the wordplay.
'knight' becomes 'sir' (a knight has the title Sir).
'to look' becomes 'lo' (archaic exclamation meaning 'look!').
'fashionable' becomes 'in' (in can mean fashionable or trendy).
'sir'+'lo'+'in'='SIRLOIN'
'with' acts as a link.
(Other definitions for sirloin that I've seen before include "(Knighted?) cut of meat" , "Upper part of loin of beef" , "Type of steak" , "Choice cut of beef" , "Good cut of beef" .)