Serious error, against the odds, in GCSE Greek (7)
I believe the answer is:
sincere
'serious' is the definition.
(similar in meaning)
'error against the odds in gcse greek' is the wordplay.
I cannot really understand how this works, but
'error' could be 'sin' (a sin is a moral error) and 'sin' is found in the answer.
The remaining letters 'cere' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for sincere that I've seen before include "Without deceit, genuine" , "Candid" , "Genuine; deceit-free" , "Lacking in deceit" , "Pure" .)