The term 'OPENING IN A LEAF' can be solved by the word 'STOMA', which is a five-letter word. A STOMA is a small opening in the epidermis of a leaf, stem, or other plant organ that allows for the exchange of gases and water vapor. Stomata are essential for photosynthesis, as they allow carbon dioxide to enter the leaf and oxygen to escape. They also help regulate the amount of water lost from the plant.