Cutting beam (5)
I believe the answer is:
laser
'cutting beam' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for laser that I've seen before include "Device producing an intense light beam - kind of sailing dinghy" , "Device producing a narrow, intense beam of light" , "scientific device" , "Coherent light beam" , "Source of light; type of printer" .)