"Mama" Cass Elliot, born Ellen Naomi Cohen, was a member of the group "The Mamas and the Papas." They were known for such songs as "California Dreamin'" and "Monday, Monday."
I like this as a nickname for a boy or a girl. It would be great for a girl if her name is Cassandra or Cassidy, great for a boy if his name is Casper. I don't know why those names aren't more popular. They sound nice and come with this awesome nickname.