The phrase "were acquainted with" can be replaced with a number of synonyms, each of which conveys a similar meaning. Some of the most common synonyms for "were acquainted with" include "knew," "were familiar with," "had met before," "had a relationship with," and "were introduced to." Each of these synonyms can be used to describe a level of familiarity or connection between individuals. Whether the relationship is casual or more significant, these synonyms can be effective in conveying the depth and nature of the connection between two people. Choosing the right synonym depends on the specific context and message that the writer wants to convey.