Synonyms: unidentifiable
Definition: impossible to identify
Similar words: elusive
Definition: difficult to describe
Usage: a haunting elusive odor
Similar words: intangible
Definition: hard to pin down or identify
Usage: an intangible feeling of impending disaster
Similar words: unclassifiable
Definition: not possible to classify
Similar words: undiagnosable
Definition: not possible to diagnose
Similar words: unrecognisable, unrecognizable
Definition: defying recognition as e.g. because of damage or alteration