Etymology

From kawabonga, bad; altered to cowabunga by Australian surfers and popularized by Snoopy of Peanuts, Cookie Monster of Sesame Street, and by the Teenage Mutant Ninja Turtles in their TV and movie incarnations. The Simpsons is erroneously credited with popularizing "cowabunga"; although the word appeared on early Simpsons merchandise, it was only ever included in the show to mock the misunderstanding. This expression was first used on The Howdy Doody Show and penned by the show's script and music writer, Edward G. Kean.

Interjection

1. an expression of surprise or amazement, often followed by "dude"

   Cowabunga, dude! Look at that crazy Godzilla!