愛妾[aishou] beloved concubine
妾腹[shoufuku] illegitimate (e.g. born to a mistress)
妻妾[saishou] one's wife and mistress(es)
男妾[danshou] male paramour
妾出[shoushutsu] illegitimate (e.g. born to a mistress)

妾宅[shoutaku] house in which a mistress is kept
蓄妾[chikushou] keeping a mistress (concubine)
外妾[gaishou] foreigner's mistress
洋妾[youshou] Westerner's mistress