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Webster 1913 Edition

Adj.

Not acquainted.

Cowper.

Not usual; unfamiliar; strange.

[Obs.]

And the

unacquainted

light began to fear.

Spenser.

Adj.

Not well known; unusual.

And th' unacquainted light began to fear. [Not in use.]

Not having familiar knowledge; followed by with.

My ears are unacquainted with such bold truths.

unacquainted ‎(comparative more unacquainted, superlative most unacquainted)

unacquainted in The Century Dictionary, The Century Co., New York, 1911
unacquainted in Webster’s Revised Unabridged Dictionary, G. & C. Merriam, 1913