That's a great word -- gobsmacked. I don't know what it means but I like it!
It's Brit slang. "Gob" basucally refers to the mouth.
As in: "Shut yer gob!"
Being "gobsmacked" refers to someone who is so surprised and shocked by something, that it is as if they were hit in the mouth, and unable to speak from the shock of it. (whatever caused the stunned amazement.)
Or, *actually* hit in the mouth...
:o)