Officer had lain next to the room (11)
I believe the answer is:
chamberlain
'officer' is the definition.
The definition and answer can be both people as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'lain next to the room' is the wordplay.
'next to' is a charade indicator (letters next to each other).
'the room' becomes 'chamber' (chamber is a kind of room).
'lain' after 'chamber' is 'CHAMBERLAIN'.
'had' is the link.
Can you help me to learn more?
(Other definitions for chamberlain that I've seen before include "corporation's treasurer" , "Court official - former prime minister" , "gave service to monarch once?" , "Prime minister, 1937-40" , "Old PM" .)