The C in Crt, or __ Ray Tube
Puzzle 5 of Spy World Medium Pack
Question is: The C in Crt, or __ Ray Tube
and the answer is: CATHODE
Word Meaning:
CATHODE — (electricity) An electrode, of a cell or other electrically polarized device, through which a positive current of electricity flows outwards (and thus, electrons flow inwards). It can have either a negative or a positive voltage with respect to anode of the same polarized device (depending on whether the device is a load or a source, respectively).
Definitions from Wiktionary.