Synonyms for Loneliness (same or very similar meaning)
WordNet sense 1 (the state of being alone in solitary isolation):
solitarinessWordNet sense 2 (sadness resulting from being forsaken or abandoned):
desolation, forlornnessWordNet sense 3 (a disposition toward being alone):
lonesomeness, solitude, alonenessFrom the ODE community, based on WordNetadd/edit