Source : Webster's Revised Unabridged Dictionary (1913)

Gast \Gast\, v. t. [OE. gasten, g?sten to frighten, akin to
   Goth. usgaisjan. See {Aghast}, {Ghastly}, and cf. {Gaze}.]
   To make aghast; to frighten; to terrify. See {Aghast}. [Obs.]
   --Chaucer. Shak.