PARIS—Helene de Ponsay hadn’t heard the word “femicide” until April, when police found the body of her older sister, Marie-Alice Dibon, stuffed in a suitcase, thrown into the Oise River. The 53-year-old Dibon, a pharmaceuticals and cosmetics specialist, was the 51st woman in France to be murdered by her partner in 2019. More than 50 deaths later, the word is hard to miss: in headlines, in presidential speeches, and plastered on buildings in cities across the country. Women’s rights advocates are now calling for femicide to be inscribed into the penal code.

“How shameful that it took until now,” de Ponsay said in an interview. “If we don’t define something, it doesn’t exist. Our society has systematically denied this reality.” ...