Departures could be set about eleven (5)
I believe the answer is:
exits
'departures' is the definition.
(exit is a kind of departure)
'could be set about eleven' is the wordplay.
'could be' is an anagram indicator.
'about' means one lot of letters goes inside another.
'eleven' becomes 'xi' (roman numeral).
'set' with letters rearranged gives 'ets'.
'ets' placed around 'xi' is 'EXITS'.
(Other definitions for exits that I've seen before include "Goes out, leaves" , "Ways out" , "Withdraws" , "Departs" , "Leaves the stage" .)