lost

The definition of lost is missing or unable to be found or it can mean something that was wasted or not used in a valuable way.

(adjective)

An example of lost used as an adjective is lost money which means money that has vanished due to a bad investment.
An example of lost used as an adjective is a lost opportunity which means a promising chance that someone didn't take.

Lost is defined as the past tense of to lose.

(verb)

An example of to have lost something is to have misplaced the car keys.

See lost in Webster's New World College Dictionary

transitive verb, intransitive verb

adjective

1. destroyed or ruined physically or morally
2. Theol. damned; reprobate
not to be found; missing
no longer held or possessed; parted with
no longer seen, heard, or known: a person lost in a crowd
not gained or won; attended with defeat
having wandered from the way; uncertain as to one's location
bewildered or ill at ease
not spent profitably or usefully; wasted
spent away from one's place of work, as because of illness: to make up lost time

See lost in American Heritage Dictionary 4

verb

Past tense and past participle of lose.

adjective

Unable to find one's way: a lost child.
a. No longer in the possession, care, or control of someone or something: a lost pen.
b. No longer in existence; vanished or spent: lost youth.
c. No longer known or practiced: a lost art.
d. Beyond reach, communication, or influence: The expedition was lost to the world for two months.
Not used to one's benefit or advantage: a lost opportunity.
Having not been or unlikely to be won; unsuccessful: a lost battle; a lost cause.
Beyond recovery or redemption; fallen or destroyed: a lost soul.
a. Completely involved or absorbed; rapt: lost in thought.
b. Bewildered or confused: I'm lost—can you start over?