alack (interj.) Look up alack at Dictionary.com
expression of sorrow or dismay, mid-15c. contraction of ah, lack, which according to Skeat is from lack (n.) in its secondary Middle English sense of "loss, failure, fault, reproach, shame." According to OED, originally an expression of dissatisfaction, later of regret or unpleasant surprise. Sometimes extended as alackaday ("alack the day").