My waterproof shoe? A pound wasted (4)
I believe the answer is:
gosh
'my' is the definition.
(both are expressions of surprise)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for gosh that I've seen before include "Crikey" , "Exclamation of surprise" , "Well I never!" , "Cor!" , "Good heavens!" .)