ABACK
aback
(adverb) by surprise; “taken aback by the caustic remarks”
aback
(adverb) having the wind against the forward side of the sails; “the ship came up into the wind with all yards aback”
Source: WordNet® 3.1
Etymology 1
Adverb
aback (not comparable)
(archaic) Towards the back or rear; backwards. [First attested prior to 1150.]
(archaic) In the rear; a distance behind. [First attested prior to 1150.]
By surprise; startled; dumbfounded. (see usage)
(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. [First attested in the late 17th century.]
Usage notes
• (by surprise): Preceded by a form of the word take, see take aback.
Etymology 2
Noun
aback (plural abacks)
(obsolete) An abacus.
Source: Wiktionary
A*back", adv. Etym: [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.
2. Behind; in the rear. Knolles.
3. (Naut.)
Definition: Backward against the mast;-said of the sails when pressed by
the wind. Totten. 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.
Ab"ack, n.
Definition: An abacus. [Obs.] B. Jonson.
Source: Webster’s Unabridged Dictionary 1913 Edition