levirate: the biblical institution whereby a man must marry the widow of his childless brother in order to maintain the brother's line
institution: a custom that for a long time has been an important feature of some group or society
nim: game in which matchsticks are arranged in rows and players alternately remove one or more of them; in some versions the object is to take the last remaining matchstick on the table and in other versions the object is to avoid taking the last remaining matchstick on the table