Used by one needing a rest or billiard cue (8,5)
I believe the answer is:
shooting stick
'cue' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe there's an association between them I don't understand?
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for shooting stick that I've seen before include "Mobile seat" , "Portable seat" , "Walking kit with handle that can make a small seat" , "Combined walking aid and seat" , "basic seating" .)