Sunday Best is a term that has been around for centuries and primarily used to describe one's best clothing to be worn to church. Here are some synonyms for Sunday Best; Formalwear, Sunday dress, Sunday clothes, dress-up, best bib and tucker, Sunday-go-to-meeting clothes, finery, dress clothes, tea dress, dressy. All these synonyms convey one's effort to dress respectfully especially for church attendance. There's a sense of importance and significations attached to one's choice of clothing for church-going. With the above synonyms, you should have multiple options to choose from when describing your best clothing for church or any important event.