ˌperəˈkärdēəm noun
( plural pericar·dia -ēə)
Etymology: New Latin, from Greek perikardion, neuter of perikardios around the heart, from peri- + kardia heart — more at heart
1. : the conical sac of serous membrane that encloses the heart and the roots of the great blood vessels of vertebrates and consists of an outer fibrous coat that loosely invests the heart and is prolonged on the outer surface of the great vessels except the inferior vena cava and a double inner serous coat of which one layer is closely adherent to the heart while the other lines the inner surface of the outer coat, the intervening space being filled with pericardial fluid
2. : a cavity or space that contains the heart of an invertebrate and in arthropods is a part of the hemocoele and contains blood which passes directly from it into the heart through the ostia in the walls of the latter