Old sheep outside wanders about (5)
I believe the answer is:
roams
'wanders about' is the definition.
(I've seen this in another clue)
'old sheep outside' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'sheep' becomes 'rams' (male sheep).
'outside' indicates putting letters inside.
'o' placed within 'rams' is 'ROAMS'.
(Other definitions for roams that I've seen before include "Wanders about, rambles" , "Is traveller" .)