Side-ring EXTRA · Clean speech
Tanna de-vei R’ Yishmael (cited by Torah Temimah on the adjacent 15:23, and directly relevant to why these passukim use “moshav” rather than “merchav” for a woman).
English: The school of R’ Yishmael taught: A person should always speak in clean language — for regarding the zav Scripture called it “riding-saddle” (merchav), and regarding a woman it called it “seat” (moshav).
Lashon nekiyah
Even in technical impurity law, the Torah models refined speech: the same functional article is named differently when the subject is a woman, teaching a standing ethic of clean language.