As per Hindu legend, once a demon by name Bhasmasura did penance.
Shiva granted him a boon that when he touches anyone's head, the person would turn to ashes.
Bhasmasura wanted to test the boon and wanted to touch 
the head of Shiva.
A bewildered Shiva ran to seek the favour of Vishnu, who took the form of damsel Mohini.
She lured Bhasmasura with her dance and made Bhasmasura touch his head with his hand.
The demon Bhasmasura was thus defeated.
The place where Mohini lured (meaning Moham) came to be known as Thirumohur.

According to another legend, there was a fight between the Devas (gods) and Asuras (demons) during the churning of the Ocean of Milk for Amrita (ambrosia).
Asuras were able to overpower Devas and the Devas sought Vishnu's help.
Vishnu appeared as Mohini to lure the asuras and gave them empty pot.
It is believed that Thirumohur is the place of the event.
As per Hindu legend, once a demon by name Bhasmasura did penance. Shiva granted him a boon that when he touches anyone's head, the person would turn to ashes. Bhasmasura wanted to test the boon and wanted to touch 
the head of Shiva. A bewildered Shiva ran to seek the favour of Vishnu, who took the form of damsel Mohini. She lured Bhasmasura with her dance and made Bhasmasura touch his head with his hand. The demon Bhasmasura was thus defeated. The place where Mohini lured (meaning Moham) came to be known as Thirumohur.
According to another legend, there was a fight between the Devas (gods) and Asuras (demons) during the churning of the Ocean of Milk for Amrita (ambrosia). Asuras were able to overpower Devas and the Devas sought Vishnu's help. Vishnu appeared as Mohini to lure the asuras and gave them empty pot. It is believed that Thirumohur is the place of the event.
Thirumohoor Kalamegaperumal temple