allantochorion

noun
al·​lan·​to·​cho·​ri·​on | \ ə-ˌlan-(ˌ)tō-ˈkōr-ē-ˌän, -ˈkȯr- How to pronounce allantochorion (audio) \

Medical Definition of allantochorion

: an embryonic membrane consisting of a fused allantois and chorion