The phrase "to gain private ends" refers to the act of pursuing personal interests for personal gain rather than the greater common good. There are several synonyms that represent this concept such as self-serving, selfish, egoistic, opportunistic, insincere, and mercenary. Self-serving implies seeking one's own interests at the expense of others. Selfish suggests a disregard for the needs and interests of others. Egoistic suggests a narrow focus on one's own needs or desires. Opportunistic implies taking advantage of situations for personal gain. Insincere suggests a lack of honesty or authenticity in one's actions. Mercenary implies a willingness to do whatever is necessary for financial gain. Using these synonyms allows for a more nuanced understanding of the motivations behind pursuing personal interests.