Peg out in allotment finds incline (8)
I believe the answer is:
gradient
'incline' is the definition.
(I've seen this before)
'peg out in allotment' is the wordplay.
'peg out' becomes 'die'.
'in' indicates putting letters inside.
'allotment' becomes 'grant' (grant is a kind of allotment).
'die' placed into 'grant' is 'GRADIENT'.
'finds' acts as a link.
(Other definitions for gradient that I've seen before include "Third OT book" , "Perhaps one in ten" , "Inclination" , "Degree of slope in a road" , "Slope or incline" .)