“Whoa” is hardly a new word; it dates back to at least the early 17th century. At that time it was used mostly in shouted form and was intended to garner the attention of someone in the distance. Around the the mid-1800s, people began using “whoa” to halt forward-moving horses, and by the latter half of the 20th century it had morphed into an expression for conveying alarm, surprise, or advanced interest. (Messrs. Bill and Ted solidified the strength of this usage in 1989, Joey Lawrence sealed the deal during the ’90s, and Keanu Reeves reappeared without Bill S. Preston, Esq. to help usher the word into the new millennium via The Matrix.)
Whoa! Woah?! Whoah. – How an old exclamation became the Internet’s most variously spelled word. (via Coudal)
onlinecollegedegreee.blogspot.com A History of Whoa! Woah!