tetrode

/T EH1 T R OW0 D/
noun
  1. 1

    A thermionic valve similar to a triode with the addition of a screen grid to protect the control grid.

  2. 2

    A dynatron.

  3. 3

    A dual-gate MOSFET.

Source: https://en.wiktionary.org/wiki/tetrode