From disaster + -ous, after Middle French desastreux (modern French désastreux; from desastre (modern French désastre, “disaster”; from des- + astre, a calque of Italian disastro) + -eux), itself after Italian disastroso, from disastro + -oso, from dis- (“away, without”) (from Latin dis-) + astro (“star, planet”) (from Latin astrum (“star, celestial body”), from Ancient Greek ᾰ̓́στρον (ắstron)).