'Month' in the Bible

Then Esther was taken to King Ahasuerus at his royal residence in the tenth month (that is, the month of Tebeth) in the seventh year of his reign.

In the first month (that is, the month of Nisan), in the twelfth year of King Ahasuerus' reign, pur (that is, the lot) was cast before Haman in order to determine a day and a month. It turned out to be the twelfth month (that is, the month of Adar).

So the royal scribes were summoned in the first month, on the thirteenth day of the month. Everything Haman commanded was written to the king's satraps and governors who were in every province and to the officials of every people, province by province according to its script and people by people according to its language. In the name of King Ahasuerus it was written and sealed with the king's signet ring.

Letters were sent by the runners to all the king's provinces stating that they should destroy, kill, and annihilate all the Jews, from youth to elderly, both women and children, on a particular day, namely the thirteenth day of the twelfth month (that is, the month of Adar), and to loot and plunder their possessions.

The king's scribes were quickly summoned -- in the third month (that is, the month of Sivan), on the twenty-third day. They wrote out everything that Mordecai instructed to the Jews and to the satraps and the governors and the officials of the provinces all the way from India to Ethiopia -- a hundred and twenty-seven provinces in all -- to each province in its own script and to each people in their own language, and to the Jews according to their own script and their own language.

This was to take place on a certain day throughout all the provinces of King Ahasuerus -- namely, on the thirteenth day of the twelfth month (that is, the month of Adar).

In the twelfth month (that is, the month of Adar), on its thirteenth day, the edict of the king and his law were to be executed. It was on this day that the enemies of the Jews had supposed that they would gain power over them. But contrary to expectations, the Jews gained power over their enemies.

The Jews who were in Susa then assembled on the fourteenth day of the month of Adar, and they killed three hundred men in Susa. But they did not confiscate their property.

All of this happened on the thirteenth day of the month of Adar. They then rested on the fourteenth day and made it a day for banqueting and happiness.

This is why the Jews who are in the rural country -- those who live in rural cities -- set aside the fourteenth day of the month of Adar as a holiday for happiness, banqueting, holiday, and sending gifts to one another.

to have them observe the fourteenth and the fifteenth day of the month of Adar each year

as the time when the Jews gave themselves rest from their enemies -- the month when their trouble was turned to happiness and their mourning to a holiday. These were to be days of banqueting, happiness, sending gifts to one another, and providing for the poor.