atrocity n.

*āter-, Proto-Indo-European root meaning "fire." It forms all or part of: atrabiliary; atrabilious; atrium; atrocious.

It is the hypothetical source of/evidence for its existence is provided by: Old Persian atar "fire;" Latin ater "black" ("blackened by fire"), atrox "frightful" ("of fiery or threatening appearance").

Proto-Indo-European root meaning "to see."

It forms all or part of: amblyopia; antique; antler; atrocity; autopsy; binocle; binocular; biopsy; catoptric; Cyclops; daisy; enoptomancy; eye; eyelet; ferocity; hyperopia; inoculate; inveigle; monocle; monocular; myopia; necropsy; ocular; oculist; oculus; oeillade; ogle; ophthalmo-; optic; optician; optics; optometry; panoptic; panopticon; Peloponnesus; pinochle; presbyopia; prosopopeia; stereoptican; synopsis; triceratops; ullage; wall-eyed; window.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit akshi "the eye; the number two," Greek osse "(two) eyes," opsis "a sight;" Old Church Slavonic oko, Lithuanian akis, Latin oculus, Greek okkos, Tocharian ak, ek, Armenian akn "eye."

1660s, "heinous, extremely criminal, enormously cruel," from stem of Latin atrox "fierce, savage, cruel" (see atrocity) + -ous. The weakened colloquial sense of "very bad" is by late 19c. Related: Atrociously; atrociousness.