Source : Webster's Revised Unabridged Dictionary (1913)

Placental \Pla*cen"tal\, a.
   1. Of or pertaining to the placenta; having, or characterized
      by having, a placenta; as, a placental mammal.

   2. (Zo["o]l.) Of or pertaining to the Placentalia.

Placental \Pla*cen"tal\, n. (Zo["o]l.)
   One of the Placentalia.

Source : WordNet®

placental
     adj : of or having or occurring by means of a placenta; "all
           mammals except monotremes and marsupials are placental
           mammals" [ant: {aplacental}]

placental
     n : mammals having a placenta; all mammals except monotremes and
         marsupials [syn: {placental mammal}, {eutherian}, {eutherian
         mammal}]