UNICITY
Noun
unicity (usually uncountable, plural unicities)
The state or quality of being unique or one of a kind.
The fact of being united as a whole.
Synonyms
• oneness
• uniqueness
Source: Wiktionary
U*nic"i*ty, n. Etym: [L. unicus single. See Unique.]
Definition: The condition of being united; quality of the unique;
unification.
Not unity, but what the schoolmen call unicity. De Quincey.
The unicity we strive not to express, for that is impossible, but to
designate by the nearest analogy. Coleridge.
Source: Webster’s Unabridged Dictionary 1913 Edition