From 雌(めす) (mesu, “female animal; vulgar: female person”) + 堕(お)ち (ochi, “連(れん)用(よう)形(けい) (ren'yōkei, “stem or continuative form”) of the verb 堕(お)ちる (ochiru).”).
めすおち or メスおち • (mesu-ochi)