expression, noun-modifying (irregular)
strange; unfamiliar; mysterious; suspicious
Fixed prenominal expression meaning something or someone is of unknown identity, origin, or nature, often with a negative or uneasy nuance. Equivalent to 得体の知れない.
See also: 得体の知れない
A strange man was standing in front of the house.
He contracted a mysterious illness.
From 得体 (identity, nature) + の + 知れぬ (archaic negative of 知れる, 'to be known'). The phrase literally means 'whose nature is not known'.