What is the definition or description of: nail bruise?

Hematoma?: Bleeding under the nail is almost always caused by trauma. It can be quite painful as the fingertips have lots of nerve endings causing pain. The bleeding under the nail can separate the nail from the underlying nailbed, but the nail usually regrows. But it can take 4-6 months. If there has been no trauma, discoloration under the nail can rarely be due to a type of skin cancer. Get checked out.