Allies' foe (4)
I believe the answer is:
axis
'allies' foe' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for axis that I've seen before include "On which a body spins" , "Feasible" , "Imaginary line about which a body rotates and a Dublin theatre" , "Line of symmetry" , "Centre about which something turns" .)