making great mental demands; hard to comprehend or solve or believe
difficult to detect or grasp by the mind or analyze
difficult to describe
skillful at eluding capture
not openly made known
conducted with or marked by hidden aims or methods
hidden from general view or use
not expressed
(of information) given in confidence or in secret
having an import not apparent to the senses nor obvious to the intelligence; beyond ordinary understanding
something that baffles understanding and cannot be explained
designed to elude detection
information known only to a special group
communicated covertly
indulging only covertly
not open or public; kept private or not revealed
something that should remain hidden from others (especially information that is not to be passed on)
the next to highest level of official classification for documents
