Denoting two or more progeny of a multiple pregnancy that have shared a common amniotic sac. ... (05 Mar 2000) ... 
(mon″o-am″ne-ot´ik) having or developing within a single amniotic cavity; said of monozygotic twins.
Type: Term Pronunciation: mon′ō-am′nē-ot′ik Definitions: 1. Denoting two or more progeny of a multiple pregnancy that have shared a common amniotic sac.
Sharing one amniotic sac in the uterus; applied to twins