bulb vs thermionic valve

bulb

noun
  • A light bulb (not necessarily bulbous in shape). 

  • Any solid object rounded at one end and tapering on the other, possibly attached to a larger object at the tapered end. 

  • A bulbous protuberance at the forefoot of certain vessels to reduce turbulence. 

  • The bulb-shaped root portion of a plant such as a tulip, from which the rest of the plant may be regrown. 

verb
  • To take the shape of a bulb; to swell. 

thermionic valve

noun
  • An electronic device incorporating electrons from a glowing cathode inside an evacuated glass tube, functioning as a switch, amplifier etc. 

How often have the words bulb and thermionic valve occurred in a corpus of books? (source: Google Ngram Viewer )