多妻 is read as たさい (tasai) and means polygamy.
たさい
tasai
いっぷたさい
polygamy
いっぷたさいせい
polygyny
いっさいたふ
polyandry
たすう
majority
たよう
diverse
たぼう
being very busy
たにんず
large number of people
たようか
diversification
たすうけつ
majority decision
talented
ためん
many-sided
たなん
full of troubles, difficulties