The word hematoma means “pocket of blood.” The term subungual means “under the nail.” Combined, the phrase refers to a pocket of blood trapped under a fingernail or toenail. Subungual hematomas often result from a traumatic injury such as slamming a finger in a door. A laceration of the nail bed causes bleeding into the constricted area underneath the hard nail plate. The nail develops a black discoloration above the laceration.