Learn That Word

Synonyms for Lightless (same or very similar meaning)

WordNet sense 1 (impossible or nearly impossible to see; imperceptible by the eye):
invisible, unseeable

WordNet sense 2 (without illumination):
unlighted, unlit, unilluminated

WordNet sense 3 (devoid of or deficient in light or brightness; shadowed or black):
dark


From the ODE community, based on WordNetadd/edit