adv

• (archaic, Geordie) Towards the back or rear; backwards.
  "The mild, though licentious reign, of Louis the Sixteenth, threw France far aback, in her ambitious career; but it gave birth to that revolution, wherein, her warlike propensities and territorial resources were unfolded with tenfold efficacy."
• (archaic) In the rear; a distance behind.
  "There are so many canes upon Reliance that the labourers could not cut those aback, as they prefer cutting those in front. The cane fields aback were in cultivation last year."
• (nautical) Backward against the mast; said of the sails when pressed by the wind from the "wrong" (forward) side, or of a ship when its sails are set that way.
  "Q. Was not the Trident at that time aback with one or more Top-sails? A. To the best of my Knowledge she had both Top-sails aback."

noun

• (obsolete, Early Modern) An inscribed stone square.
  "In the Centre, or midst of the Pegm, there was an Aback, or Square, wherein this Elogy was written."