undetected
unknown
able
enigmatic
hidden
incalculable
incognizable
invisible
mysterious
puzzling
sealed
strange
unapparent
unapprehended
unascertained
unbeknown
uncharted
unclassified
undisclosed
undiscoverable
undivulged
unexplained
unexplored
unexposed
unfamiliar
unfathomed
unheard
unheard-of
unidentified
uninvestigated
unknowable
unperceived
unplumbed
unrevealed
unseen
unsolved
unspied
unsuspected
untouched
untraced
untracked
virgin
dormant
inaccessible
northwestern
unclaimed
uncollected
unconquered
undeveloped
unfelt
unguessed
unimagined
unmapped
unobserved
unoccupied
unrecognized
unreported
untapped
untried
untrodden
covered
discovered
hovered
recovered
rediscovered
uncovered