Gee whiz! (4)
'gee whiz' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for gosh that I've seen before include "Exclamation of surprise" , "Crikey" , "Wow!" , "expression of surprise" , "I'm amazed!" .)
(Another definition for golly that I've seen is " Gosh!".)