Pi representing something that goes on forever? (10,3)
I believe the answer is:
bottomless pit
'something that goes on forever?' is the definition.
(pit going on forever)
'pi' is the wordplay.
I cannot quite see how this works, but
'pi' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
'representing' is the link.
(Other definitions for bottomless pit that I've seen before include "Source of infinite fuel" , "place needing it eternally" , "nether regions - with 7a" .)