Origin: Latin suffix -al
Placental has 4 different meanings across 2 categories:
mammals having a placenta; all mammals except monotremes and marsupials
Any animal that is a member of the Placentalia
pertaining to or having or occurring by means of a placenta
"all mammals except monotremes and marsupials are placental mammals"
Of or pertaining to the placenta, or to the Placentalia