Use it to aim a gun, that makes sense! (5)
I believe the answer is:
sight
This could be a double definition.
'use it to aim a gun that' is the first definition.
The answer and definition can be both acts as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'sense' is the second definition.
(sight or vision is a sense)
'makes' acts as a link.
Can you help me to learn more?
(Other definitions for sight that I've seen before include "Show" , "Field of vision" , "24" , "object of especial interest" , "Looking" .)