The difference between Impersonal and Unipersonal

When used as adjectives, impersonal means not personal, whereas unipersonal means comprising a single person.

check bellow for the other definitions of Impersonal and Unipersonal

Impersonal as an adjective:

Not personal; not representing a person; not having personality.

Examples:

"An almighty but impersonal power, called Fate.'' –Sir J. Stephen."
Impersonal as an adjective:

Lacking warmth or emotion; cold.

Examples:

"She sounded impersonal as she gave her report of the Nazi death camps."
Impersonal as an adjective (grammar, of a verb or other word):

Not having a subject, or having a third person pronoun without an antecedent.

Examples:

"The verb “rain” is impersonal in sentences like “It’s raining.”"