Wandering man about desert (7)
I believe the answer is:
erratic
'wandering' is the definition.
(I know that wandering can be written as erratic)
'man about desert' is the wordplay.
'man' becomes 'eric' (I've seen this before).
'about' indicates putting letters inside.
'desert' becomes 'rat' (abandon treacherously).
'eric' enclosing 'rat' is 'ERRATIC'.
(Other definitions for erratic that I've seen before include "Wild" , "Behaving irregularly" , "Irregular and unreliable" , "Fluctuating" , "Hit-or-miss" .)