Was sound, if unoriginal (6)
I believe the answer is:
echoed
'unoriginal' is the definition.
The answer and definition are not the same part of speech. However, adjectives and past participle verbs sometimes define each other.
'was sound' is the wordplay.
I cannot quite see how this works, but
'sound' could be 'echo' (echoing is a kind of sounding) and 'echo' is located in the answer.
The remaining letters 'ed' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'if' is the link.
Can you help me to learn more?
(Other definitions for echoed that I've seen before include "Resounded" , "said nothing original" , "Reverberated; repeated" , "Rang" , "Repeated a sound" .)