Informal, Brit. astounded, stunned, etc.
Origin of gobsmackedfrom British slang gob, the mouth + smack
adjectiveChiefly British Slang
Extremely surprised or shocked; astounded: I was gobsmacked to learn that my cousin is a spy.
Origin of gobsmackedgob 2 smack 1 -ed 2
(comparative more gobsmacked, superlative most gobsmacked)
gobsmacked - Computer Definition
A British term meaning to be completely astonished about something.