"Rudraksa" means the eye of Rudra or Siva. "Rudraksa-mala" is a "garland" (or rosary) made up of such "eyes". "Aksa" means eye. In Tamil the rudraksa is called "tirukkanmani"[ the sacred pupil of the eye]
What is the meaning of "aksamala" or "sphatika-aksamala"? Here the word "aksa" is not taken to mean the eye but the letters of the alphabet from "a" to "ksa". In the Sanskrit alphabet "a" comes first and "ksa" comes last. To learn the "A" to "Z" of a subject means to have a thorough grasp of it. To convey the same idea in Sanskrit we say "a-karadi ksa-karantam". There are 50 letters from "a" to "ksa". So an aksamala consists of 50 beads. There is of course a 51st bead which is bigger than the rest and it is called "Meru". The sun, the legend goes, does not go beyond the Meru mountain during his daily journey. When we make one round thus, muttering the name of the Lord or a mantra, first clockwise up to the Meru and then anticlockwise up to the Meru again, we will have told the beads a hundred times.
For a general background, please see here