Your father’s wife: this means any wife of the father other than the mother of the person spoken to here, since the matter of one’s own mother has already been dealt with in the previous verse. Some languages have completely different words for “mother” and “stepmother.” Good News Translation translates the meaning clearly with “any of his other wives.”

Quoted with permission from Péter-Contesse, René and Ellington, John. A Handbook on Leviticus. (UBS Helps for Translators). New York: UBS, 1990. For this and other handbooks for translators see here .