Sly has stiffener — way to go (4)
I believe the answer is:
arch
'sly' is the definition.
(I've seen this before)
'stiffener way to go' is the wordplay.
'stiffener' becomes 'starch' (starch is used to make fabric stiff).
'way' becomes 'st' (abbreviation for street).
'to go' indicates named letters should be taken away.
'starch' with 'st' removed is 'ARCH'.
'has' acts as a link.
(Other definitions for arch that I've seen before include "This could be Wellington" , "Prefix meaning chief - maybe an angel" , "Knowing, coy" , "Way though - on foot!" , "Affectedly playful or extreme" .)