"Yippee!” (5)
(Other definitions for wahoo that I've seen before include "Burning bush" , "swimmer" , "in America, yeah baby!" , "Ornamental shrub" , "Large fish related to the mackerel" .)
'yippee' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for hooray that I've seen before include "Joyous exclamation" , "Hurrah" , "Cheer" , "Exclamation of joy or victory" , "Shout of joy (for Henry?)" .)
(Other definitions for oh boy that I've seen before include "Blimey!" , "Expression of enthusiasm, pleasure, etc" .)