General synonyms:
* Missing
* Gone
* Misplaced
* Strayed
* Vanished
* Absent
* Unfound
Synonyms related to specific contexts:
* Confused (if referring to being lost in thought or direction)
* Despair (if referring to feeling lost in life)
* Ruined (if referring to something lost and unrecoverable)
* Defeated (if referring to a lost battle or competition)
* Doomed (if referring to something lost with no chance of retrieval)
The best synonym for "lost" will depend on the specific situation and the intended meaning.