zygocardiac (?za?????k??d?æk) adj (Zoology) zoology relating to a small bone in the stomach of a crayfish and other crustaceansCollins English Dictionary ? Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014