Skeleton in the closet
Meaning: A shameful or embarrassing secret
Originated in: 🇬🇧 United Kingdom
Earliest attestation: "Adams on Epidemic Diseases, &c." by Joseph Adams, M.D. The Eclectic Review, Volume 6 (1816)
Having a skeleton in the closet means having a shameful or embarrassing secret that you are trying to hide. The phrase is used to describe a secret that could ruin someone’s reputation if it were revealed. Somewhat often it is used somewhat literally to describe the belief that someone is a murderer, but generally it is purely figuratively, as having a skeleton in your home is quite taboo whether you killed him or not.
The idea of a skeleton in the closet comes from the idea of literally having a skeleton hidden in your closet, waiting to be discovered. That raises the question of why someone other than a murderer would have a skeleton hidden in his home. Historically, possessing a cadaver was illegal in the Christian world as it was seen as disrespecting the dead. Various Christian universities still performed dissections to study human anatomy, but it was not something an ordinary person was allowed to do.
As medical science advanced and more people had more questions about anatomy, laws were widened to allow more dissections. In England specifically, Henry VII allowed four executed people to be dissected per year. Elizabeth I increased this to eight. Yet more people continued going into medicine and they did not have enough bodies to teach with. Thus the Murder Act 1751 required that all murderers people either be dissected or the body be hung in chains from a gibbet to further discourage the crime. This greatly increased the supply of cadavers for a while, but the number of doctors kept increasing and the number of murders actually did decrease, making the body supply stretched thin again.
During this time, many would-be doctors began acquiring corpses of non-criminals even though it was illegal. The night after funerals, grave robbers would go out and dig up the bodies to loot and sell to medical schools. Many medical students had to hide these bodies well until they could be studied and disposed of. Thus this idiom arose. Not only was having the freshly-dug-up body of an innocent person taboo, it was also a criminal misdemeanor. Eventually, the Anatomy Act 1832 allowed doctors and medical students to freely dissect donated bodies, but the decades of secrecy left its idiomatic mark regardless.
Like you would judge a person for having a body in his house so long it decomposed to just a skeleton, so you would judge a person for having a metaphorical skeleton in his closet. It describes a secret that is not only shameful, but also one that has been concealed for a long time. The phrase is sometimes used in a lighthearted way, but often it is used for terrible secrets that could have serious consequences if they were revealed.