Rashi on Deuteronomy 22:11/רש"י על דברים כ״ב:י״א

1שעטנז is an expression for a mixture. Our Rabbis explained it to mean a material that is calendered (pressed, שוע), or woven (טווי), or twisted (נוז) together (Sifrei Devarim 232:1); (שעטנז is taken to be an abbreviation of these words; cf. Rashi on Leviticus 19:19 and our Note thereon).