Aback
ABACK, adverb [At, on or towards the back. See Back]
Towards the back; on the back part; backward. In seamen's language it signifies the situation of the sails, when pressed back against the mast by the wind.
Taken aback is when the sails are carried back suddenly by the wind.
Laid aback is when the sails are purposely placed in that situation to give the ship sternway.