Source of support, but not backing! (5)
I believe the answer is:
stool
'backing' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'source of support but not' is the wordplay.
I cannot quite see how this works, but
'of' could be 'o' and 'o' is present in the answer.
'not' could be 'o' (I've seen this in other clues) and 'o' is found within the answer.
The remaining letters 'stl' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for stool that I've seen before include "Backless chair" , "place butt on one?" , "Motion" , "item of furniture here" , "Three-legged backless seat" .)