Microdots are tiny coded messages that have been used for espionage and communication. There are several synonyms for microdots that can be used interchangeably, depending on the context. One synonym is "minuscule dots," which accurately describes the small size of these messages. Another synonym is "hidden messages," which conveys the secretive nature of the messages and their purpose. "Invisible ink" is another synonym that highlights the covert element of microdots. "Subtle symbols" can also be used to describe microdots, as they are subtle messages hidden within a larger document. Lastly, "encrypted dots" provides a technical and precise term for microdots.