Not familiar or acquainted with another.(adjective)
Not informed or knowledgeable: unacquainted with the legal issues at hand. (adjective)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "unacquainted" in a sentence
"[Page 98] tempted to reveal matters with which, for the happiness of others, it is much better the public should remain unacquainted."
"Describing the cherished Hindu festival of Holi to the unacquainted is a bit like explaining the Fourth of July or Thanksgiving."
"But death in its more sordid and terrible aspects was a thing with which I had been unacquainted till now."