Involucrum is a term used in anatomy and refers to a protective structure that forms around a bone that has been infected or affected by a disease. There are several synonyms that can be used to describe this structure, including shell, casing, covering, sheath, capsule, envelope, coat, and wrapper. Each of these synonyms highlights the protective function of the involucrum and suggests a level of insulation from external factors. The word "involucrum" is commonly used in medical contexts, but these synonyms may be useful in everyday language when describing other protective structures, such as a phone case or a protective layer around sensitive equipment.