One that might ring corporation? It's not unknown (4)
I believe the answer is:
bell
'one that might ring' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'corporation? it's not unknown' is the wordplay.
'corporation?' becomes 'belly' ('belly' can be a synonym of 'corporation').
'it's not' suggests deleting specific letters.
'unknown' becomes 'y' (algebra).
'belly' with 'y' removed is 'BELL'.
Can you help me to learn more?
(Other definitions for bell that I've seen before include "Wide end of a trumpet" , "End of oboe; inventor of telephone" , "He invented" , "Stag's cry; ringer" , "ring" .)