Black tie is a traditional dress code for formal events, but there are other suitable synonyms that can also be used to convey the same level of formality. One option is 'white tie', which is even more formal than black tie and often reserved for diplomatic or royal events. Another synonym is 'evening dress', which includes the same black tie attire for men and formal gowns for women. 'Formal dress' or 'formal attire' are also commonly used to refer to black tie dress code, while 'dress suit' is an old-fashioned term that is still sometimes used. Whatever the synonym used, the key is to understand the level of formality required for the event and dress accordingly.