a cathode-arc vacuum tube with an auxiliary electrode projecting into a pool of mercury: it conducts current when the anode is positive.
Origin of ignitron
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
a mercury-arc rectifier controlled by a subsidiary electrode, the igniter, partially immersed in a mercury cathode. A current passed between igniter and cathode forms a hot spot sufficient to strike an arc between cathode and anode
Word Origin for ignitron
C20: from igniter + electron
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012