When referring to someone or something as "like a maiden aunt," it implies that they are prim, proper, and somewhat old-fashioned. Some synonyms for this phrase include "prim and proper," "old-fashioned," "uptight," "prudish," "spinsterish," and "puritanical." These phrases all convey a certain level of conservatism and adherence to traditional values. Other synonyms could include "formal," "reserved," "prissy," and "stuffy." While some may view this type of behavior as stuffy or unexciting, others may see it as respectable and dignified. Regardless, the use of these synonyms will help to paint a clear picture of the individual or situation being described.