The term 'airtight it may be' is composed of four crossword solutions: ALIBI (5 letters), SEAL (4 letters), HERMETIC (8 letters), and silos (5 letters). An ALIBI is an excuse or explanation used to avoid blame for a crime or wrongdoing. A SEAL is a device or material used to close off an opening, such as a door or container. HERMETIC refers to something that is airtight and impervious to outside influences. Finally, silos are tall, cylindrical structures used to store grain, coal, or other materials. Together, these words describe something that is completely sealed off from the outside world.