There are many alternatives to the phrase "one night stand" depending on the context and level of formality required. Some informal synonyms can include "hookup," "fling," "booty call," or "casual encounter." On the more formal side, a person might say they had a "brief romantic dalliance" or a "short-term tryst." Other options include "one-time fling," "fleeting liaison," or a "passionate interlude." All of these phrases essentially mean the same thing, but each has its own connotations and subtle differences that may affect which one is used in a particular setting. The key is to take into account the context and audience when choosing an appropriate synonym.