and Father-in-law. The stepfather is the father of one bereaved of his natural father by death. A stepmother is the mother of one bereaved of his mother by death. A stepfather must be married to a widow, and thus become the stepfather of her children by a previous husband; and a stepmother must be married to a widower, and thus become the stepmother of his children by a former wife. Similarly, stepson and stepdaughter must be the son and daughter by the father or mother deceased, the relict marrying again.
FATHER-IN-LAW and MOTHER-IN-LAW are the father and mother of the wife to her husband, and of the husband to the wife. Similarly, sons-in-law and daughters-in-law are the sons and daughters of the parents of the wife to the husband and of the husband to the wife. (Anglo-Saxon, steop, bereaved.)
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
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