Do you know ghouls from goblins and ghosts?
1590s, from Late Latin polygamia, from Late Greek polygamia "polygamy," from polygamos "often married," from polys "many" + gamos "marriage" (see gamete). Not etymologically restricted to marriage of one man and multiple women (technically polygyny), but often used as if it were. Related: Polygamist.
The practice of having several wives or husbands at the same time. (Compare monogamy.)