No longer accepted a position in fort (7)
I believe the answer is:
outpost
'fort' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'no longer accepted a position' is the wordplay.
'no' becomes 'O' (resembles 0 - 'no' can mean 'zero').
'longer accepted' becomes 'ut' (I can't explain this - if you can you should believe this answer much more).
'a position' becomes 'post' (post is a kind of position).
'o'+'ut'+'post'='OUTPOST'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for outpost that I've seen before include "Small group of soldiers" , "Remote military camp" , "Outlying settlement" , "Remote part of an empire" , "Distant office, settlement" .)