Form small awkward heap (5)
I believe the answer is:
shape
'form' is the definition.
(I know that form can be written as shape)
'small awkward heap' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'awkward' is an anagram indicator.
'heap' is an anagram of 'hape'.
's'+'hape'='SHAPE'
(Other definitions for shape that I've seen before include "Mould into new phase" , "Form; mould" , "Heaps (anag.)" , "For good physical condition" , "Good physical form" .)