Kind of sheet (4)
I believe the answer is:
spec
'kind of sheet' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for spec that I've seen before include "work to be done" , "On - means without a plan but with hope of success" , "Awkward, clumsy" , "on which chance is taken" , "Estimate" .)