愛人

Àirén is one of those words you have to be a little careful about, as it has different meanings in different Chinese dialects. If you introduce a female acquaintance as your àirén in stodgy Beijing, she is your legally married wife. If you make your way to Taiwan and introduce her again, people will think she is your lover, more specifically a mistress. This is also the Japanese meaning for the same characters, although the pronunciation becomes aijin.

And trust me: no matter how much you love them, you do not want to introduce your children as your àirén.