Skeleton in the closet Informal

A discreditable, shameful, or embarrassing secret that someone keeps carefully hidden from public knowledge.

It’s used both for personal secrets and for organizations or families, implying that the secret would seriously damage reputation if it ever came out.

The image is of a literal human skeleton, the physical remains of a body, hidden away out of sight in a closet rather than properly buried or disclosed — something that could theoretically be produced as damning evidence at any moment. The phrase is documented in English as early as November 1816, which is worth noting because it predates by more than a decade the notorious British body-snatching scandals of the 1820s (culminating in the Burke and Hare murders of 1828) and the Anatomy Act of 1832, both of which are often loosely and anachronistically connected to this idiom in popular explanations. Given the 1816 date, the association with doctors illegally acquiring anatomical skeletons is more likely a later folk elaboration layered onto an already-existing general metaphor for hidden shame, rather than the idiom’s actual documented source.

Every family has a skeleton in the closet somewhere.

The scandal revealed a skeleton in the closet nobody expected.

He seems perfect, but I bet he’s got a skeleton in the closet.

A: Why won’t she talk about her past? B: Sounds like a skeleton in the closet to me.