allantois

noun

al·​lan·​to·​is ə-ˈlan-tə-wəs 

plural allantoides ˌa-lən-ˈtō-ə-ˌdēz 

ˌa-ˌlan-

: a vascular fetal membrane of reptiles, birds, and mammals that is formed as a pouch from the hindgut and that in placental mammals is intimately associated with the chorion in formation of the placenta

allantoic

ˌa-lən-ˈtō-ik 

ˌa-ˌlan-

adjective

Word History

Etymology

borrowed from New Latin, probably taken as singular of earlier allantoidēs in the same sense, borrowed from Greek allantoeidḗs "sausage-like" (in allantoeidḕs hymḗn "allantois," literally, "sausage-like membrane"), from allant-, allâs "sausage" (of uncertain origin) + -oeidḗs -oid entry 2

First Known Use

1615, in the meaning defined above

Medical Definition

allantois

noun

al·​lan·​to·​is ə-ˈlant-ə-wəs 

plural allantoides ˌal-ən-ˈtō-ə-ˌdēz  ˌal-ˌan- 

: a vascular fetal membrane of reptiles, birds, or mammals that is formed as a pouch from the hindgut and that in placental mammals is intimately associated with the chorion in formation of the placenta