Plane perhaps regularly turned east (4)
I believe the answer is:
tree
'plane perhaps' is the definition.
(plane is a type of tree)
'regularly turned east' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'east' becomes 'e' (abbreviation).
The alternating letters of 'turned' are 'tre'.
'tre'+'e'='TREE'
(Other definitions for tree that I've seen before include "Plane, e.g." , "Be up a .... to be in difficulties" , "Genealogy chart" , "famous actor" , "plane, say?" .)