dirty linen
US /ˈdɜːr.t̬i ˈlɪn.ɪn/
UK /ˈdɜːr.t̬i ˈlɪn.ɪn/
1.
private and embarrassing matters that one would prefer to keep secret
:
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They aired their dirty linen in public during the divorce proceedings.
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It's best not to discuss your family's dirty linen with strangers.