The word 登机 is formed by combining the character 登, meaning "to ascend" or "to board", with the character 机, which is an abbreviation for 飞机 (airplane) and means "aircraft". Together, they create a compound word where 登 acts as the verb indicating the action, and 机 serves as the object, resulting in the literal meaning "to board the aircraft", specifically referring to the process of embarking on a plane.