Grand lakeside wing appended to complete force's HQ (11)
I believe the answer is:
gendarmerie
'grand lakeside wing' is the definition.
The answer and definition can be both groups as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'appended to complete force's hq' is the wordplay.
I cannot really see how this works, but
'complete' could be 'end' (I've seen this before) and 'end' is found in the answer.
'force' could be 'g' and 'g' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for gendarmerie that I've seen before include "foreign force" , "Police force" , "Nick" , "French law keepers" , "French paramilitary police" .)