Head off for shelter? (4)
I believe the answer is:
flee
'head off for shelter?' is the definition.
Although both the answer and definition are verbs in their base form, I don't see how they can define each other.
'head off for shelter?' is the wordplay.
'head off' indicates taking the first letters.
'shelter?' becomes 'lee' (as in lee side, the side sheltered from wind).
The first letter of 'for' is 'f'.
'f'+'lee'='FLEE'
(Other definitions for flee that I've seen before include "Leave" , "Turn tail" , "Do a runner" , "Cut and run" , "head for the hills" .)