unobserved (adj.)

• camouflaged
• concealed
• disguised
• hidden
• imperceptible
• indiscernible
• insensible
• invisible
• latent
• secret
• sightless
• submerged
• unapparent
• unconsidered
• unheeded
• unmarked
• unnoted
• unnoticed
• unperceivable
• unperceived
• unrealized
• unremarked
• unseeable
• unseen
• unthought-of
• viewless