Aback /(ȧ*băk")/

A·back

Aback

adv.
  1. Toward the back or rear; backward.
  2. Behind; in the rear.
  3. Backward against the mast; -- said of the sails when pressed by the wind. (Naut.)

Phrases & Compounds
To be taken aback
To be driven backward against the mast; -- said of the sails, also of the ship when the sails are thus driven.

Aback

n.
  1. An abacus. [Obs.]