Something that's lamentable is unfortunate. If your basketball team gets killed in the final game, you could call it a lamentable way for the season to end.
Something that's not satisfactory can be described as lamentable, like a high school art room equipped with only crayons and construction paper. A person's inappropriate behavior could also be considered lamentable — whether it's the cruel words of a bully or your lack of preparation for an important speech. The Latin word lamentationem is at the root of lamentable, and it means "wailing, moaning, or weeping." If a situation is bad enough to make you cry, it's lamentable.