Source : Webster's Revised Unabridged Dictionary (1913)

Eftsoon \Eft*soon"\, Eftsoons \Eft*soons"\, adv. [OE. eftsone,
   eftsones; AS. eft + s?na soon. See {Eft}, and {Soon}.]
   Again; anew; a second time; at once; speedily. [Archaic]

         And, if he fall from his capel [horse] eftsone.
                                                  --Chaucer.

         The champion stout eftsoons dismounted.  --Spenser.