slackjawed

Adjective

slack-jawed (comparative more slack-jawed, superlative most slack-jawed)

1. With the mouth in an open position and the jaw hanging loosely, especially as indicating bewilderment or astonishment.
   • For one frightful moment there was no sound; even the men's breathing was hushed, and they sat slack-jawed, stunned, half-minded to believe this some hideous, incredible jest.1911, Rex Ellingwood Beach, chapter 26, in The Ne'er-Do-Well

   Synonyms:

   dazzled, dumbfounded, open-mouthed, stunned

2. (broadly) Unsophisticated or unthinking; dimwitted in appearance.
   • She brought to the stage the barefoot, slack-jawed frontiersmen found on postcards in every convenience store and tourist trap in the Ozarks.2002, Brooks Blevins, Hill Folks: A History of Arkansas Ozarkers and their Image, →ISBN, page 262

   Synonyms:

   dopey, stupid, stupefied

3. (dated) Overly talkative; indiscreet.
   • As a matter of fact, it was by trying to lean on it that Spencer Clay got hold of the facts of the case; and when young Clay got hold of anything, Marois Bay at large had it hot and fresh a few hours later; for Spencer was one of those slack-jawed youths who are constitutionally incapable of...1917, P. G. Wodehouse, “Wilton's Holiday”, in The Man with Two Left Feet and Other Stories

   Synonyms:

   big-mouthed