When two people know each other, they are said to be acquainted. However, when two people do not know each other, they may be considered unacquainted or unfamiliar. Other antonyms for being acquainted could include being strangers, unknown to each other, or not having crossed paths. Conversely, synonyms for being acquainted may include being familiar, meeting before, or knowing someone well. It's important to note that these terms can often be subjective and depend on the context in which they are used. For example, two people may have met briefly but not be considered fully acquainted, while others may consider that meeting enough to qualify as being acquainted.