aback

Etymology 1

From Middle English abak, from Old English onbæc, equivalent to a- (“towards”) + back. Compare West Frisian tebek (“aback”, adverb, literally “to/at back”), Swedish tillbaka (idem.).

adv

1. (archaic) Towards the back or rear; backwards.
   Al blody, and therwith-al a-bak she sterte c. 1380s, Geoffrey Chaucer, The Legend of Good Women/The Legend of Thisbe
   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. 1815, David Laurie, A Treatise on Finance, under which, the General Interests of the British Empire are Illustrated, Glasgow: Chapman, page 322
   Then stopped, and bounded aback, and away as if in fear, / That I saw her no more; then I wondered though sitting close anear / Was a she-wolf great and grisly. 1889, William Morris, A Tale of the House of the Wolfings and All the Kindreds of the Mark, London: Reeves & Turner, page 31
2. (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. 1840, “Proceedings of an Inquiry held at plantation Reliance, in the county of Essequibo”, in Papers Relative to the West Indies, 1841: British Guiana, London: H.M.S.O., published 1841, page 201
3. By surprise; startled; dumbfounded. (see usage)
   I would rather board a hundred of the enemy's frigates, than steer my boat into a fleet of modest women, for a modest woman never fails to take me aback. 1808, The Post-Captain: A View of Naval Society and Manners, 3rd edition, London: Thomas Tegg, page 165
4. (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. 1757, Charles Fearne, The Trial of the Honourable Admiral John Byng, at a Court Martial, London: Manby, et al, page 89
   As the anchor fetches her up, she will swing head to wind, bringing the head sails aback. 1841, Benjamin J. Totten, Naval Text-book, Boston: Little & Brown, page 144
   Then the sails on the mainmast were backing and we started getting stern way. Eagle was caught aback. 2001, Russell Drumm, The Barque of Saviors, Houghton Mifflin, page 91

Etymology 2

From Latin abacus.

noun

1. (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. 1604, Ben Jonson, “Part of the King's Entertainment in Passing to His Coronation”, in The Works of Ben Jonson, London: Printed by Thomas Hodgkin, published 1692, page 306