1757, French, literally "out of combat." Hors (prep.) "out, beyond," is from Latin foris (adv.) "outside," literally "out of doors" (see foreign). De is from Latin de "of." For combat see combat (n.). A similar expression from French is hors concours "out of competition" (1884), of a work of art in an exhibition.
horrific
horrify
horripilation
horror
hors d'oeuvre
hors de combat
horse
horse sense
horseback
horse-car
horse-chestnut