WordWeb Online

1. Impossible or nearly impossible to see; imperceptible by the eye
   "the invisible man"; "invisible rays"; "an invisible hinge"; "invisible mending"
   - unseeable
    
2. Not prominent or readily noticeable
   "the invisible man"
   - inconspicuous

See also: camouflaged, concealed, conspicuousness, covert, hidden, imperceptible, infrared, invisibleness, invisibly, lightless, nonvisual, obscure, occult, out of sight, ultraviolet, undetectable, unnoticeable, unperceivable, unseen

Antonym: visible

Encyclopedia: Invisible