].........I noticed that in the beginning when we are learning of John Dashwood's character, finances and his relationship to Elinor, Marianne and Margaret, JA refers to their mother has his mother in law. Really, she would be his step mother. A few paragraph's later she does call the elder Mrs. Dashwood, Fanny's mother in law.

The term "mother-in-law" was as commonly used for a step-parent as for a spouse's parent.

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