Like an impossible clue, accepting end of crossword is unable to be cracked (12)
I believe the answer is:
indissoluble
'like an impossible clue' is the definition.
(something indissoluble cannot be solved)
'accepting end of crossword is unable to be cracked' is the wordplay.
I cannot really see how this works, but
'of' could be 'o' and 'o' is located in the answer.
'is' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for indissoluble that I've seen before include "permanent!" , "That cannot be separated" .)