The Romans were intensely superstitious. Any chance event or chance remark that occurred on the eve of an undertaking was carefully examined to determine whether it might indicate good luck or bad luck.
Thus Cicero tells us that Crassus, when about to embark upon his ill-fated expedition against the Parthians, should have turned back. At the harbor, a man selling dried figs from Caunus, gave the cry, “Cauneas!” to signify the source of his wares.
This to the Romans sounded like “Cave ne eas,” meaning, “Beware of going,” which Crassus should have taken to be a sign of bad luck, an evil omen. Crassus had not heeded the warning, however, and was treacherously slain by the Parthians.
Any such omen as that was considered to have been a clear portent of doom, amply warning one to avoid whatever undertaking he had in mind. For that reason it was described as abominabilis, from ab, away from, and omen.
The early sense of the term, “direful, inspiring dread, ominous,” came through association of ideas to mean “loathsome, disgusting,” because it was usually loathsome things that were taken as omens of evil.