Word: Heavier-than-air
Part of Speech: Adjective
Simple Explanation: The term "heavier-than-air" describes something, especially an aircraft, that weighs more than the air it pushes out of the way when it flies. This means that these aircraft need special ways to lift off the ground because they cannot float like lighter-than-air objects (like balloons).
"Heavier-than-air" is an important term in aviation that refers to aircraft that weigh more than the air they displace.