It sounds like fruit (5)
I believe the answer is:
plumb
'it' is the definition.
The definition suggests a singular noun which matches the answer.
'sounds like fruit' is the wordplay.
'sounds like' indicates a 'sounds like' (homophone) clue.
'fruit' becomes 'plum' (plum is a kind of fruit).
'plum' sounds like 'PLUMB'.
Can you help me to learn more?
(Other definitions for plumb that I've seen before include "Exactly - . . . . . in the middle" , "Dead" , "For Americans, quite" , "Reach or experience, say the depths" , "Check depth of water below" .)