Form strange heaps (5)
I believe the answer is:
shape
'form' is the definition.
('shape' can be a synonym of 'form')
'strange heaps' is the wordplay.
'strange' indicates an anagram.
'heaps' with letters rearranged gives 'SHAPE'.
(Other definitions for shape that I've seen before include "Good physical form" , "Heaps (anag.)" , "For good physical condition" , "External form" , "Control development of" .)