The Collaborative International Dictionary
Placentiform
Placentiform \Pla*cen"ti*form\, a. [Placenta + -form.] (Bot.) Having the shape of a placenta, or circular thickened disk somewhat thinner about the middle.
Wiktionary
placentiform
a. (context botany English) Having the shape of a placenta, or thickened disk somewhat thinner about the middle.