Not acquainted, unfamiliar (with someone or something).
1705, William Dampier, Voyages and Descriptions, London: James Knapton, Volume 2, “Voyages to the Bay of Campeachy,” Chapter 1, p. 26,
[…] from our Main-top we saw the Islands to the Southward of us, and being unacquainted, knew not whether we might find among them a Channel to pass through […]
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