pericardium (n.)

"membranous sac which encloses the heart," early 15c., from Medieval Latin pericardium, Latinized form of Greek perikardion "(membrane) around the heart" (Galen), from peri (prep.) "around, about" (see peri-) + kardia "heart" (from PIE root *kerd- "heart"). Related: Pericardiac.