Unity is oneness, the state of being one, especially of that which never has been divided or of that which can not be conceived of as resolved into parts; as, the unity of God or the unity of the human soul.

J. C. Fernald, English Synonyms and Antonyms (1914)

Example sentences

union It is improper to impose sanctions upon the union.
unity Our unity in opposing hate speech is our strength.
individuality Individuality is stressed in the Western world.

Popularity over time

Word	1850 → 2019	Trend
oneness		rising
union		falling
unity		falling
individuality		steady
singleness		steady

Use in printed books, per decade from 1850 to 2019.

By length

5 letters: union², unity³
7 letters: unicity
8 letters: identity⁴, sameness²
10 letters: singleness
13 letters: individuality⁷

The small number after each word is its number of syllables (union² = 2 syllables).