What that might be? (8,7)
I believe the answer is:
relative pronoun
'be?' is the definition.
Both the answer and definition are singular nouns.
Perhaps you can see an association between them that I don't see?
I can't explain the rest of the clue.
(Other definitions for relative pronoun that I've seen before include "It could be that" , "Maybe what" , "Say which" .)