The term 'shut tightly' can be represented by two crossword solutions: SEAL (4 letters) and SEALED (6 letters). To 'SEAL' something means to close it securely so that nothing can enter or escape. It is often used in reference to containers, such as jars, bottles, or boxes, and can be done with a variety of materials, such as wax, tape, or glue. To be 'sealed' means that the item has been completely shut and secured.