Backward against the mast; said of the sails when pressed by the wind from the "wrong" (forward) side
By setting the foresail aback and the headsail in the middle one can bring a fore-and-aft rigged sailing boat practically to a halt even in heavy wind.
by surprise; "taken aback by the caustic remarks" having the wind against the forward side of the sails; "the ship came up into the wind with all yards aback
If you are taken aback by something, you are surprised or shocked by it and you cannot respond at once. Roland was taken aback by our strength of feeling. be taken aback (by sth) to be very surprised or shocked by something
backwards, to the rear; with the wind blowing against the front of the sails (Nautical)