Something of the same sort as 6 (which, in fact, I haven't decided on yet - it's a clue that I didn't have to) is part of the ANSWER to each clue, but is not referred to at all in the clue itself. The full definition IS given, though.
The best thing about this one was, in the middle of the night I failed to notice the special instruction & found the whole puzzle pretty frustrating! Now it's finished I must admit it's quite celever!
The really frustrating thing is I have 4 to go, can only be sure that I have 9 of the 12, and can't see how to get another 3 into the final 4. Aaarrrgghhh! Taking much longer than usual.