Perigonium is a term used in botany to describe the collective name given to the outermost layer of a flower, where the petals and sepals are located. There are several synonyms for this term, including perianth, tepal, and chlamys. The perianth is specifically used to describe the non-reproductive parts of the flower, which include the sepals and petals, while tepals are used to describe the perianth parts that are undifferentiated, meaning they cannot be classified as petals or sepals. Chlamys is another alternative term, which describes the perianth in Greek literature and mythology. While the term perigonium is widely used among botanists, these synonyms can be helpful to understand the different parts of the flower and their functions.