The name is derived from Terhenetär which was the name of an ancient Finnish goddess who appears in the epic, the Kalevala.
In the Kalevala, Terhenetär is described as a sort of sprite associated with mist and forests. Both names are derived from the Finnish, terhen, meaning, “mist.”
Terhenetär means, “mist lady” or “lady of the mist.”
Another form is Terhikki.
The designated name-day is February 6.