The Collaborative International Dictionary of English v.0.48:
Solitariness \Sol"i*ta*ri*ness\, n. Condition of being solitary. [1913 Webster]WordNet (r) 3.0 (2006):
solitariness n 1: the state of being alone in solitary isolation [syn: loneliness, solitariness] 2: a disposition toward being alone [syn: aloneness, loneliness, lonesomeness, solitariness]