An Etymological Dictionary of Astronomy and Astrophysics

Moving or able to move, operate, function, or take effect quickly; quick; swift; rapid (Dictionary.com).

Etymology (EN): M.E., from O.E. fæst “firmly fixed, steadfast;” O.Fr. fest, O.N. fastr, Du. vast, Ger. fest.

Etymology (PE): Tond “swift, rapid, brisk; fierce, severe,” → velocity.