Get the FREE one-click dictionary software for Windows
or the iPhone/iPad and Android apps
Adjective: lightless  lIt-lus
  1. Giving no light
    "lightless stars ‘visible’ only to radio antennae"
     
  2. Without illumination
    "came up the lightless stairs";
    - unilluminated, unlighted, unlit

See also: dark, invisible, unseeable