I beleive the
origin of the term 'valve' goes back to the diode, by
analogy with the one-way valve on a tyre or something like that.
I seem to remember reading somewhere that Fleming introduced the term
around 1904 for exactly that reason.
I beliece the original term was "Fleming's Oscillation Valve", as in a
device that let oscillations of one polarity through, and blocked the
ones of the other polarity.
Then of course there was the 'Audion Bulb' (an early name for the triode).
-tony