There are various synonyms for the phrase "lack of loyalty." A few commonly used ones are unfaithfulness, disloyalty, treachery, betrayal, infidelity, and perfidy. These terms all refer to a lack of allegiance or commitment, particularly in a personal or professional relationship. Whether it's a spouse cheating on their significant other or an employee divulging confidential company information, these acts show a disregard for trust and loyalty. Synonyms like these can be used interchangeably with "lack of loyalty," depending on the context. Whichever term is selected, it makes the message clear that a breach of trust has occurred and the ramifications of such actions may be far-reaching.