The tenth and the most important day of Onam celebrations is known as Thiru Onam or the Tiru Onam. Here Thiru or Tiru stands for sacred, holy, beautiful or auspicious and is equivalent of 'Sri' in Hindi. It is so called as the day is the most significant of all, for the people of Kerala. People believe that it is on the tenth day that Lord Mahabali comes to visit his people.
Some scholars say that the name Thiru Onam comes from the name Sravanotsav out of which 'Sra' was taken out and 'vana' was transformed to 'Onam'. To the word Onam, 'Thiru' was added as the asterism Sravana on which Onam is celebrated was sacred to Lord Vishnu.
Elaborate preparations are made to celebrate Thiru Onam in the grandest possible way. Early in the morning people perform special prayers to invoke divine blessings. Women clean up the house and decorate a flower mat in the front courtyard of the house. This is to welcome the spirit of the legendary King who is so much appreciated by his people centuries after his golden reign.
A grand meal called Onasadya is also prepared to impress upon the spirit of the King that his people are happy and wish him well. Thiru Onam evenings are spent playing games and indulging in cultural events. Lightening and dazzling display of fire also takes place with much fan fair.