Double-crossing is a phrase used to describe the act of betraying someone. Synonyms for this phrase include: duplicitous, deceitful, disloyal, treacherous, unfaithful, sneaky, two-faced, backstabbing, untrustworthy, and perfidious. Each of these words carries a similar meaning to double-crossing, but may have slightly different connotations. For example, "treacherous" may imply a greater degree of danger or harm, while "unfaithful" may refer specifically to breaking a promise or commitment. Regardless of the specific word used, the act of double-crossing is universally recognized as a serious breach of trust and integrity, and should be avoided at all costs.