"What fun!" (4)
'what fun' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for whee that I've seen before include "Expression of delight" , "Cry from someone going downhill fast?" , "Exclamation of excitement when going fast" , "What fun" , "Exuberant cry" .)
(Other definitions for wahoo that I've seen before include "swimmer" , "Burning bush" , "Large fish related to the mackerel" , "Ornamental shrub" , "in America, yeah baby!" .)