Sentence:  "Your plan provides Browne with two charming wives and gives me but one. ..." / "But, my lord," said Saunders, "doesn't the plan give Lady Deppingham two husbands? It's quite a fair division." / "It would make Lord Deppingham my husband-in-law, I imagine," said Drusilla quaintly. "I've always had a horror of husbands-in-law." / "And you would be my <WSD>wife-in-law</WSD>," supplemented Lady Agnes. "How interesting!" 
Meaning of the word marked with <WSD> tags:  Another wife of one's husband. Typically used in cases of divorce and subsequent remarriage for one's husband's ex-wife, but sometimes used in polygamy for a co-wife.