'slack-jawed adj having your mouth slightly open, especially because you are surprised or stupid = open-mouthed They looked at him, slack-jawed with disbelief.
1. He noticed at once that discipline was slack. 他马上觉察到敌方纪律松弛.
2. He noticed at once that discipline was slack: the Danes had the self-confidence of conquerors, and their security precautions were casual. 他马上发现丹麦军纪律松弛,他们以征服者自居,安全措施马马虎虎。