a·lack (ə-lāk') interj. Used to express sorrow, regret, or alarm: "'Las and fearful alack—nobody can make such high claims for the people then living in Maine"(John Gould).
1480, from ah, lack, from lack (q.v.) in M.E. sense of "loss, failure, reproach, shame." Originally an expression of dissatisfaction, later of regret or surprise.