Let us consult the fount of random information wikipedia:
Basilisk:
[quote=wiki]In European bestiaries and legends, a basilisk (from the Greek βασιλίσκος basiliskos, a little king, in Latin Regulus) is a legendary reptile reputed to be king of serpents and said to have the power of causing death by a single glance. According to the Naturalis Historia of Pliny the Elder, the basilisk is a small snake that is so venomous that it leaves a wide trail of deadly venom in its wake, and its gaze is likewise lethal.[/quote]
King of the reptiles, usually either a lizard or a snake, wiht a death gaze.
Cockatrice:
[quote=wiki]A cockatrice is a legendary creature, "an ornament in the drama and poetry of the Elizabethans" (Breiner). The cockatrice was invented in the late twelfth century based on a hint in Pliny's Natural History, as a duplicate of the basilisk or regulus, in appearance resembling a giant rooster, with a lizard-like tail. It was supposed to be born from an egg laid by a cock[1] and incubated by a toad or serpent. Attempts to identify it with any particular biological species, often of snakes, have proved generally futile and it is generally considered a bogey of the wasteland.[/quote]
A duplicate creature, thinly plagiarised from the basilisk as early as the 12th century in europe. However, it possesses it's own appearence, features, backgrounds, and weaknesses as distinct to from the basilisk.
Perhaps 900 years ago they were almost the same, however, since the split they each have developed into entirely seperate beasts in the realms of fantasy. A simple example would be that an adventuring party equipped and prepared to fight a cockatrice would be met with a rude surprise and perhaps death should they come up against a basilisk instead. [/DnDgeekishness]
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