Convivant

[Tanya Shivari]

A significant other who is a live in partner. A [domestic] partner. A name you give someone who is more than just your boyfriend or girlfriend and not quite your [spouse]. [Con]~ latin for with; vivir~ latin for live.

[Julene]

live in [boy or girl] friend, [significant other], [unmarried]

[Raeanne Dimick]

Source: This word was introduced by Simon [Winchester] on [NPR]. (Maybe on Oct-14-2002, Talk of [the Nation] )