Pi won't break your fall (10,3)
I believe the answer is:
bottomless pit
'won't break your fall' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.
'pi' is the wordplay.
I cannot quite understand how this works, but
'pi' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for bottomless pit that I've seen before include "Source of infinite fuel" , "nether regions - with 7a" , "place needing it eternally" .)