Incline the head (3)
I believe the answer is:
nod
'incline the head' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for nod that I've seen before include "'A . . . is as good as a wink to a blind horse'" , "Cain left Eden for the Land of . . ." , "Appear to fall asleep" , "Green light" , "Gesture of assent" .)