One fixedly attached to a firearm (7)
I believe the answer is:
bayonet
'a firearm' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'one fixedly attached' is the wordplay.
I cannot really understand how this works, but
'one' could be 'a' (a thing is one thing) and 'a' is present in the answer.
'attached' could be 'on' (I've seen this in other clues) and 'on' is present in the answer.
This explanation may well be incorrect...
'to' acts as a link.
Can you help me to learn more?
(Other definitions for bayonet that I've seen before include "Type of light bulb fitting" , "Rifle attachment" , "one's attached to one's rifle - that's sort of fitting" , "Dagger attached to 26 Across" , "Neat boy (anag.)" .)