It's all in vain since relic is not genuine (9)
I believe the answer is:
insincere
'not genuine' is the definition.
(I've seen this before)
'it's all in vain since relic' is the wordplay.
'INSINCERE' is hidden within the letters.
However, I'm unsure how this is indicated.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for insincere that I've seen before include "Not genuine, feigned" , "Not expressing genuine feelings" , "Feigned, smarmy" , "Dissembling" , "Untruthful" .)