placental adjective 2noun 1forms 1 adjective2 •Of or pertaining to the placenta. •Pertaining to the Placentalia, comprising of mammals that are not marsupials or monotremes.We do not know exactly how many placental lineages survived to leave descendants; most estimates are around ten. — 2022 noun1 •A mammal of the infraclass Placentalia. formsplacentals
