The word nefarious comes from the Latin “nefastus” formed from the negation “ne” and the word “fastus” that alludes to the day when justice could be administered, a term derived from an Indo-European root; then etymologically it could be said that disastrous is used to describe those days in which public business could not be carried out. And it is, according to the Roman calendar, where this particular use is given to the words "fastus" and "nefastus" to designate the days in which citizens were allowed to take charge of justice; and for their part, disastrous were the days when they were not allowed to carry out such activity.
The dictionary of the real Spanish academy states that disastrous refers to the day, week, months or any other period of time assigned as fatal, abominable, hateful, disgusting, sad. In other words, at that time, that is, for the time of the Roman Empire, the disastrous days were those proposed as days of mourning, or during which all kinds of commemorations were held on different unpleasant events.
Nowadays the meaning for the word grim is generally used to cite a day or a certain moment of it that is characterized by being sad or fateful for a particular reason. Although at present it is also applied to qualify an individual or a thing, which from our point of view and for different reasons is unhappy, detestable or unfortunate.
