It's unoriginal, we hear (4)
I believe the answer is:
echo
'it's' is the definition.
I can't tell whether this definition defines the answer.
'unoriginal we hear' is the wordplay.
'unoriginal' means to remove the first letter (original (starting) letter removed).
'hear' becomes 'cho' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'we' with its first letter removed is 'e'.
'e'+'cho'='ECHO'
Can you help me to learn more?
(Other definitions for echo that I've seen before include "Response" , "She loved Narcissus - it's recalled" , "Repetition of sound" , "call back" , "copy" .)