According to www.Armeniapedia.org
“The name Tamar comes from an Armenian folklore of the legend of Akhtamar Island:
An Armenian princess named Tamar lived on Akhtamar Island in Lake Van (in Historic Armenia). She was in love with a commoner. This boy would swim from the mainland to the island each night, his way lit by a light she lit for him. One day her father found out about this and was very upset. He went to her as she held the light, waiting for her love. He smashed her light, leaving the boy in the middle of the lake without an idea of which direction to swim. They say his dying cries of Akh, tamar…(Oh, Tamar) can be heard to this day at night. This is where the name of the island comes from.