in·vo·lu·crum \ˌ ̷ ̷ ̷ ̷ˈ ̷ ̷krəm\noun (pluralinvolu·cra \-krə\) Etymology: Latin, from involvere to wrap, envelop 1.: a surrounding envelope or sheath < each group has its involucrum of space from which it drives any encroaching group — C.S.Coon > 2.[New Latin, from Latin]: involucre 3.[New Latin, from Latin]: a formation of new bone about a sequestrum (as in osteomyelitis)