Definition of Placentalia in US English:

Placentalia

noun

Zoology
  • With singular concord: a division of mammals comprising those in which the females develop a placenta, equivalent to the infraclass Eutheria. Treated as plural: placental mammals collectively; eutherians, as distinguished from marsupials and monotremes.

Origin

Mid 19th century; earliest use found in William T. Brande (1788–1866), chemist. From scientific Latin Placentalia, use as group name of neuter plural of placentalis, adjective.

Pronunciation

Placentalia

/ˌplas(ə)nˈteɪlɪə/