"Holy smokes!" (4)
(Other definitions for whoa that I've seen before include "halt" , "Opposite of "Giddy-up!"" , "Said to stop a horse" , "Hold your horses!" , "Cry for horses to stop" .)
(Other definitions for wow that I've seen before include "Expression of surprised admiration" , "Expression of amazement" , "Cor! - huge success" , "Palindrome exclamation of astonishment or admiration" , "Palindromic exclamation of surprise or admiration" .)