This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

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n. The state or quality of being solitary.

n. Condition of being solitary.

n. The fact or state of being solitary, or alone, or without mate, partner, or companion, or of dwelling apart from others or by one's self; habitual retirement; solitude.

n. The state or character of being retired or unfrequented; solitude; seclusion: as, the solitariness of a wood.

n. the state of being alone in solitary isolation

n. a disposition toward being alone

"I may not deny but that there is some profitable meditation, contemplation, and kind of solitariness to be embraced, which the fathers so highly commended, [1562] Hierom, Chrysostom, Cyprian,"

isolation   

wariness   

friendlessness    primness    converser    separateness    meagreness    ceremoniousness    ferociousness    impracticability    self-conquest    sombreness