The Collaborative International Dictionary of English v.0.48:

Tetrasyllabic \Tet`ra*syl*lab"ic\, Tetrasyllabical
\Tet`ra*syl*lab"ic*al\, a. [Cf. F. t['e]trasyllabique.]
   Consisting of, or having, four syllables; quadrisyllabic.
   [1913 Webster]