The internal structure composed of bone and cartilage that protects and supports the soft organs, tissues, and other parts of a vertebrate organism; endoskeleton. The hard external supporting and protecting structure in many invertebrates, such as mollusks and crustaceans, and certain vertebrates, such as turtles; exoskeleton. A supporting structure or framework, as of a building. An outline or sketch. Something reduced to its basic or minimal parts. One that is very thin or emaciated. Of, relating to, or resembling a skeleton. Reduced to the basic or minimal parts or members: a skeleton crew. skeleton in (one's) closet A source of shame or disgrace, as in a family, that is kept secret.