/ ˌʌnəˈkaʊntɪd fɔː(r); NAmE / adjective [ not before noun ]
1.
a person or thing that is unaccounted for cannot be found and people do not know what has happened to them or it :
At least 300 civilians are unaccounted for after the bombing raids.
2.
not explained :
In the story he gave the police, half an hour was left unaccounted for.