1
general::
A hopeless undertaking, as in Trying to get him to quit smoking is a lost cause. In the 1860s this expression was widely used to describe the Confederacy. [Mid-1800s] Also see LOSING BATTLE.
American Heritage Idioms
2
general::
Phrase(s): a lost cause
a futile attempt; a hopeless matter. • Our campaign to have the new party on the ballot was a lost cause. • Todd gave it up as a lost cause.
McGrawhill's American Idioms And Phrasal Verbs