The Collaborative International Dictionary
Implacental
Implacental \Im`pla*cen"tal\, a. (Zo["o]l.) Without a placenta, as marsupials and monotremes; nonplacental. -- n. A mammal having no placenta; a nonplacental mammal.
Wiktionary
implacental
a. (context zoology English) Without a placenta, as marsupials and monotremes. n. (context zoology English) A mammal having no placenta.