Stiff untanned leather (7)
I believe the answer is:
rawhide
'stiff untanned leather' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for rawhide that I've seen before include "Whip" , "Untanned animal skin cut to make whips and ropes" , "Stiff untanned leather" , "Leather before tanning" .)