The Collaborative International Dictionary of English v.0.48:

Syntony \Syn"to*ny\, n. [Cf. Gr. ? agreement. See Syn-;
   Tone.] (Physics)
   State of being adjusted to a certain wave length; agreement
   or tuning between the time period of an apparatus emitting
   electric oscillations and that of a receiving apparatus, esp.
   in wireless telegraphy.
   [Webster 1913 Suppl.]