1. Having the wind against the forward side of the sails
   "the ship came up into the wind with all yards aback"
    
2. By surprise
   "taken aback by the caustic remarks"

Encyclopedia: Aback

• unfreeze
• unfrequented
• unfretted
• unfriended
• unfriendliness
• unfriendly
• unfrightened
• unfrock
• unfrosted
• unfrozen
• unfruitful
• unfueled
• unfuelled
• unfulfillable
• unfulfilled
• unfunctional
• unfunded
• unfunny
• unfurl
• unfurnished
• unfurrowed
• ungainliness
• ungainly
• ungallant
• ungarbed