The term 'PART OF THE CALYX OF A FLOWER' can be summarized by the word 'SEPAL', which is a five-letter word. Sepals are the outermost layer of a flower, and they are typically green and leaf-like in appearance. They are part of the calyx, which is the collective term for all of the sepals of a flower. Sepals serve to protect the inner parts of the flower, such as the petals and reproductive organs.