The term "well-acquainted" signifies a strong relationship between two individuals. There are various synonyms for this expression that denote familiarity, such as versed, known, and conversant. Other words that can be used to describe a similar relationship include familiar, intimate, and closely associated. These terms have slightly different connotations, but all imply a high level of connection and understanding between two people. Close, well-informed, and knowledgeable are also commonly used synonyms that reflect a deep level of personal connection and understanding. Overall, there are many words to express this concept that varies slightly in tone or emphasis, but they all indicate a relationship that has gone beyond simply being introduced.