adj : (British; informal) utterly astounded
This is a wonderful expression for indicating astonishment. It seems to have mostly stayed in the UK, but I would guess that most people would get the intent if you employed the expression on this side of the pond.
gob
"a mouthful, lump," c.1382, from O.Fr. gobe "mouthful, lump," from gober "gulp, swallow down," probably from Gaul. *gobbo- (cf. Ir. gob "mouth," Gael. gob "beak"). This Celtic source also seems to be root of gob "mouth" (c.1550), which is the first element in gob-stopper "a kind of large hard candy" (1928).