The Collaborative International Dictionary of English v.0.48:

colliding-beam machine \colliding-beam machine\ n. (Physics)
   a particle accelerator in which two separate beams of
   particles (usually of opposite charge) are circulated in
   opposite directions and directed so as to collide head on; --
   called also colliding-beam accelerator and collider.

   Note: This technique allows the production of collisions of
         higher energy than would be possible with a single beam
         produced by the same device.

   Syn: particle collider; colliding-beam accelerator; collider.
        [WordNet 1.5 +PJC]