missing (of a person); lost; unaccounted for; whereabouts unknown
of uncertain meaning; ambiguous; cryptic; nonsensical; incomprehensible; perplexing
unidentifiable; unidentified
untraceable; long lost; one's whereabouts being unknown
(a person or body being) unidentifiable (unidentified)
inaccurate; indistinct; imprecise; unclear; indecisive
of unknown nationality (of a vessel, plane, etc.); unidentified
unclear point; unclear points
dubious; doubtful; of unknown authenticity
unaccounted-for expenditures
fate (safety) of a person (persons) being unknown
without a place of publication; sine loco; s.l.
the point of an argument being unclear; the tenor of an argument being poorly reasoned