Aback

• having the wind against the forward side of the sails; "the ship came up into the wind with all yards aback"
• by surprise; "taken aback by the caustic remarks"
• An abacus; Towards the back or rear; backwards; away; Behind; in the rear; Backward against the mast; said of the sails when pressed by the wind
• Wind filling the sail from the opposite direction to that intended. If a sail fills correctly the boat moves forwards.
• A sail pushed back by the wind, so it slows the forward motion of the cat. (A jib purposely trimmed to windward is "backwinded", not aback)