an exclamation of delight or satisfaction
from Chief Thunderthud on the Howdy Doody Show
1954, American English, from exclamation of surprise and anger by "Chief Thunderthud" in "The Howdy Doody Show," 1950s children's TV show; used by surfers 1960s as a shout of triumph, and spread worldwide 1990 by use in the TV cartoon "Teenage Mutant Ninja Turtles."
A surfer's exclamation of delight and commitment at the beginning of a ride, often used as a generalized cry of delight: It was the real Andy Griffith, too: cowabunga (1950s+ Surfers)
Energetic popular plaudits: make their most open bid yet for commercial cowabunga (1980s+)
[apparently coined by Eddie Kean, writer of the television Howdy Doody Show, as a distress call for one of the characters]