Webster's Revised Unabridged Dictionary · 1913

Eftsoon

Eftsoon , adverb

[Old English eftsone, eftsones; Anglo-Saxon eft + sōna 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

Also: Eftsoons