The term 'It's Lighter than Air' can be solved by two crossword solutions: DIRIGIBLE (9 letters) and Ammonia (7 letters). A DIRIGIBLE is a type of airship, or a large aircraft that is powered by engines and steered by a crew. It is filled with a gas that is lighter than air, such as hydrogen or helium, which allows it to float in the sky. Ammonia is a chemical compound made up of nitrogen and hydrogen atoms. It is also lighter than air, and is often used as a lifting gas in airships.