The Collaborative International Dictionary of English v.0.48:

CRO \CRO\ n. (Electronics)
   acronym for cathode-ray oscilloscope, an electronic device
   which provides visual images of varying electrical
   quantities. See oscilloscope.

   Syn: oscilloscope, scope, cathode-ray oscilloscope.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

CRO
    n 1: electronic equipment that provides visual images of varying
         electrical quantities [syn: oscilloscope, scope,
         cathode-ray oscilloscope, CRO]