most illusive

The Americans are not naive about the chances of achieving the most illusive of goals in the Middle East, amid some of the worst bloodshed in the region's modern history.

And what of Ludwig Wittgenstein, the most illusive and therefore most interesting of the philosophical wizards?

For just as you, on your side of the theory of knowledge, are busy in trying to account for your Ideas, so they, on theirs, have much ado in their efforts to account for you; all of them find you the most illusive of beings, while some, as I have already hinted, deny your existence altogether, or treat you as a highly questionable hypothesis.

She carried on with him a regular cross-fire of witticisms, of mocking and sarcastic sallies, of that most illusive and treacherous kind that, smoothly wrapped up on the surface, hit the mark without giving the victim anything to lay hold of, and exhaust him in fruitless efforts to repel the attack, reducing him to fury and comic despair.

The mystery of the disease was most illusive.