Set out about eleven leaves (5)
I believe the answer is:
exits
'leaves' is the definition.
('exit' can be a synonym of 'leave')
'set out about eleven' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'about' is an insertion indicator.
'eleven' becomes 'xi' (Roman numerals).
'set' anagrammed gives 'ets'.
'ets' going around 'xi' is 'EXITS'.
(Other definitions for exits that I've seen before include "Departs" , "Withdraws" , "Egresses" , "Leaves the stage" , "Goes out, leaves" .)