The definition of alack is a word used to express sorrow or regret.
(interjection)An example of a time that someone might use the word alack is when he is expressing regret for letting the girl of his dreams get away.
See alack in Webster's New World College Dictionary
interjection
Origin: a(h) + lack
See alack in American Heritage Dictionary 4
interjection
Origin:
Origin: On the model of alas; see lack
.