Entry 1 sense Webster, 1913 Pericardium · Per·i·car·di·um · IPA /ˌpɛɹɪˈkɑː(ɹ)di.əm/ 01 n. The double baglike fold of serous membrane which incloses the heart. 1. The double baglike fold of serous membrane which incloses the heart.(Anat.)