"Tis" is a contraction of the archaic phrase "it is". There are several synonyms for this word that can be used interchangeably, including "it's", "it has", and "it hath". Additionally, the word "tis" can be replaced with more modern expressions like "that's", "that has", and "that is". In formal writing, it is often recommended to avoid using contractions altogether, and instead opt for the full phrase "it is". However, in casual conversations and informal writing, using synonyms like "tis" can help convey a more relaxed and conversational tone. Ultimately, the best synonym for "tis" depends on the context and audience.