inamorata

noun

Etymology: Borrowed from Italian innamorata, the feminine form of innamorato (“lover, boyfriend”), from innamorare (“to make somebody fall in love”), from in- (“in”) + amore (“love”).

1. A female lover or woman with whom one is in love; a mistress.

   “Presently Monsieur Margot made his appearance. Though very much surprised at seeing me, he did not appear the least jealous of my attentions to his inamorata.”