It hurts if you miss it and hit it (4)
I believe the answer is:
nail
'it hurts if you miss it' is the definition.
The definition suggests a singular noun which matches the answer.
'and hit it' is the wordplay.
I cannot quite see how this works, but
'and' could be 'n' (common abbreviation for 'and') and 'n' is found within the answer.
The remaining letters 'ail' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for nail that I've seen before include "Brad, say" , "Measure of cloth" , "Part of finger" , "thing for keeping things together" , "'For want of a . . . . the shoe was lost'" .)