Having happened or originated in a time so long ago that it has been completely forgotten or lost. / (science fiction) Lost during time travel.

(historical, US) A small, uninhabited portion of land that was left over after the division and organization of the large former Dakota Territory remnants into five new states in the late 19th century, which was overlooked by the federal government for years. It was located at the tripoint between the current states of Idaho, Wyoming, and Montana.

plural of lost river

(hydrology) A surface stream which flows into an underground passageway.

Alternative spelling of long-lost

plural of lost cause

simple past tense and past participle of lose time

plural of lost soul

(law) Income that a plaintiff in a lawsuit would have received but for the actions of the defendant, and for which the defendant is therefore liable.

(idiomatic) Synonym of fool's errand