ˈslack-jawed BrE AmE adjective
having your mouth slightly open, especially because you are surprised or stupid SYN open-mouthed :
They looked at him, slack-jawed with disbelief.
ˈslack-jawed BrE AmE adjective
having your mouth slightly open, especially because you are surprised or stupid SYN open-mouthed :
They looked at him, slack-jawed with disbelief.
Longman Dictionary of Contemporary English. Longman - Словарь современного английского языка. 2012