Slack-Jawed Meaning

(idiomatic, dated, of a person) Overly talkative; indiscreet.

Example: 1911, Rex Ellingwood Beach, The Ne'er-Do-Well, ch. 26:
  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.
2002, Brooks Blevins, Hill Folks: A History of Arkansas Ozarkers and their Image, ISBN 9780807853429, p. 262:
  She brought to the stage the barefoot, slack-jawed frontiersmen found on postcards in every convenience store and tourist trap in the Ozarks.
2005, Michelle Cottle, "My Roving Barcalounger," Time, 24 July:
  But driving a car—particularly the supersize models—really should demand more concentration than, say, slouching slack-jawed in front of the wide screen in your den.
1917, P. G. Wodehouse, "Wilton's Holiday" in The Man with Two Left Feet and Other Stories:
  Spencer was one of those slack-jawed youths who are constitutionally incapable of preserving a secret.