That’s amazing! (3)
(Other definitions for gee that I've seen before include "Alphabet's seventh letter" , "Urge horse - expression of surprise" , "Gracious" , "Expression of mild surprise (mainly US)" , "Golly" .)
(Other definitions for wow that I've seen before include "Expression of amazement" , "Exclamation of admiration - another palindrome" , "Expression of great admiration" , "boy" , "Palindromic exclamation of surprise or admiration" .)
'that's amazing' is the definition.
(expression of surprise)
This is all the clue.
(Other definitions for whoa that I've seen before include "Call to stop" , "horsy expression?" , "Said to stop a horse" , "Command for horse to slow or stop" , "Opposite of "Giddy-up!"" .)