The Collaborative International Dictionary of English v.0.48:
lightlessness \lightlessness\ n. total absence of light; blackness. Syn: total darkness, blackness. [WordNet 1.5]WordNet (r) 3.0 (2006):
lightlessness n 1: total absence of light; "they fumbled around in total darkness"; "in the black of night" [syn: total darkness, lightlessness, blackness, pitch blackness, black]