What's the difference between wivern and wyvern?

Wivern

Definition:

• (n.) A fabulous two-legged, winged creature, like a cockatrice, but having the head of a dragon, and without spurs.
• (n.) The weever.

Example Sentences:

Wyvern

Definition:

• (n.) Same as Wiver.

Example Sentences:

• (1) Bauer is now understood to be the preferred bidder for Heart 106 in the east Midlands, and BRMB, Beacon, Mercia and Wyvern in the West Midlands.