Definition of "roc"

"By this time the sun was about to set, and all of a sudden the sky became as dark as if it had been covered with a thick cloud. I was much astonished at this sudden darkness, but much more when I found it occasioned by a bird of a monstrous size, that came flying toward me. I remembered that I had often heard mariners speak of a miraculous bird called Roc, and conceived that the great dome which I so much admired must be its egg. In short, the bird alighted, and sat over the egg. As I perceived her coming, I crept to the egg, so that I had before me one of the legs of the bird, which was as big as the trunk of a tree. I tied myself strongly to it with my turban, in hopes that the roc next morning would carry me with her out of this desert island. After having passed the night in this condition, the bird flew away as soon as it was daylight, and carried me so high, that I could not discern the earth;

The Arabian Nights Entertainment. Tale 4. Sinbad. The Second Voyage.