The term 'PART OF THE CALYX' can be answered with the word 'SEPAL', which is a five-letter word. Sepals are the outermost parts of a flower's calyx, which is the collective term for the sepals, petals, and other structures that form the protective layer around the flower's reproductive organs. Sepals are typically green and leaf-like in appearance and can vary in size and shape depending on the species of flower.