WordNet (r) 3.0 (2006):

Geiger counter
    n 1: counter tube that detects ionizing radiations [syn: Geiger
         counter, Geiger-Muller counter]

Moby Thesaurus II by Grady Ward, 1.0:

21 Moby Thesaurus words for "Geiger counter":
   Wilson chamber, alpha pulse analyzer, atom counter, boron counter,
   cloud chamber, cosmic ray counter, counting tube,
   electronic counter, electrophotometer, expansion chamber,
   gamma ray counter, heavy particle counter, infrared telescope,
   ion counter, ionization chamber, particle counter,
   photoelectric counter, photoelectric recorder,
   photoelectric sorter, spectrophotometer, tube counter