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 an anagram (out can mean wrong or inaccurate).
'about' means one lot of letters goes inside another.
'eleven' becomes 'xi' (Roman numerals).
'set' anagrammed gives 'ets'.
'ets' placed around 'xi' is 'EXITS'.
(Other definitions for exits that I've seen before include "Departs" , "Withdraws" , "Egresses" , "Leaves the stage" , "Goes out, leaves" .)