The Collaborative International Dictionary of English v.0.48:

Agast \A*gast"\, p. p. & a.
   See Aghast.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Agast \A*gast"\ or Aghast \A*ghast"\, v. t.
   To affright; to terrify. [Obs.] --Chaucer. Spenser.
   [1913 Webster]

V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

AGAST
       Adventure Game Authoring SysTem