Old sheep outside for wander (4)
I believe the answer is:
roam
'wander' is the definition.
('roam' can be a synonym of 'wander')
'old sheep outside' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'sheep' becomes 'ram' (ram is a kind of sheep).
'outside' indicates putting letters inside.
'o' going into 'ram' is 'ROAM'.
'for' acts as a link.
(Other definitions for roam that I've seen before include "Prowl" , "Rove or ramble" , "Peregrinate" , "Stray" , "Meander" .)