aback

adv. [ Pref. a- + back; AS. on bæc at, on, or toward the back. See Back. ] 1. Toward the back or rear; backward. “Therewith aback she started.” Chaucer. [ 1913 Webster ]

2. Behind; in the rear. Knolles. [ 1913 Webster ]

3. (Naut.) Backward against the mast; -- said of the sails when pressed by the wind. Totten. [ 1913 Webster ]

To be taken aback. (a) To be driven backward against the mast; -- said of the sails, also of the ship when the sails are thus driven. (b) To be suddenly checked, baffled, or discomfited. Dickens. [ 1913 Webster ]