a.

1. 不知道的；不認識的；不熟悉的[F][（+with）]
   The foreigners are unacquainted with our custom.

   這些外國人不了解我們的風俗。

   He was unacquainted with that aspect of the question.

   他不了解問題的那個方面。

adj.

1. (unacquainted with) having no experience of or familiarity with.
2. not having met before.