Departs in seaplane, possibly here? (9)
I believe the answer is:
esplanade
'here?' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'departs in seaplane possibly' is the wordplay.
'departs' becomes 'd' (common abbreviation e.g. train timetables).
'in' indicates putting letters inside.
'possibly' indicates an anagram.
'seaplane' is an anagram of 'esplanae'.
'd' inserted within 'esplanae' is 'ESPLANADE'.
(Other definitions for esplanade that I've seen before include "Seaside walkway" , "Level seashore walkway" , "place for a stroll" , "Walkway beside the seashore" , "Long wide pavement next to a beach" .)