I've thought about this a lot. I considered "con" for constants. I don't hate it. It also works as a double entendre-- "con" in Spanish means "with". So the following code could be read as "with name equal to Brad".

  con name = 'Brad'

I can't help but feel that it's somewhat jarring though.

If I had my druthers, I think I would choose "var" and "def" to declare mutable and immutable variables, respectively.

  def PI = 3.1
  def degreesToRadians = degrees => degrees * (PI / 180)

  var degrees = 180
  var radians = degreesToRadians(degrees)

Edit: After thinking about it some more, I think I prefer "const" over "con", but "def" over both.