9 is Prophet and fool (10)
I believe the answer is:
seersucker
'9' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'prophet and fool' is the wordplay.
'prophet' becomes 'seer' (I've seen this before).
'and' means one lot of letters go next to another.
'fool' becomes 'sucker' ('sucker' can be a synonym of 'fool'**).
'seer'+'sucker'='SEERSUCKER'
'is' acts as a link.
(Other definitions for seersucker that I've seen before include "Material" , "Puckered fabric" , "Cotton" .)