Tag on is an idiomatic expression used to refer to the act of adding something to the end of a sentence or a discourse. There are many ways to express this idea in English, depending on the context and the level of formality required. Some of the most common synonyms for tag on include append, tack on, addendum, supplement, postscript, afterthought, annex, and endorsement. These words can be used interchangeably with tag on in many situations, but each one may convey a slightly different shade of meaning. For example, append and tack on suggest a more mechanical or abrupt addition, whereas postscript and afterthought imply a more informal or spontaneous approach to communication.