A skeleton in the cupboard is something that might bring shame or embarrassment to a family or person if other people knew about it.
Examples of use:
1. Does your family have a skeleton in the cupboard?
2. Politicians should not have any skeletons in their cupboards.
2. Did you hear about Mr Short's skeleton in the cupboard? He was sent to prison for fraud in 1984.
Skeleton in the cupboard is used in British and Australian English: skeleton in the closet is more common in American English.
More skeleton idioms:
• a skeleton key is a key that can open many different locks.
• a skeleton at the feast is a reminder of a sad or troublesome past event at a happy event or celebration.
Image © Ed Bierman