A landing ground, not a flying machine
In American English, an airdrome is a place from which aircraft operate: a field with runways, hangars, workshops, and often a passenger or cargo terminal. Dictionaries list it beside airport and beside the chiefly British spelling aerodrome. In ordinary United States speech the word now sounds dated. Airport became the default name for a civil terminal after the First World War, and airdrome lives on mainly in older military writing, historical narrative, and the occasional technical inventory of fields.
The meaning is terrestrial. The word names the ground and its buildings, not the craft that use them. That distinction matters because the parent form aerodrome once meant both, and only one of those senses survived into the American spelling.
An American recasting
The origin of the word airdrome is an alteration, not a fresh coinage from nowhere. Late in the 1910s, American usage took the established aviation noun aerodrome and replaced the Greek combining form aero- with the everyday English noun air. Merriam-Webster dates first known use of the altered spelling to 1917. Other desk dictionaries place it in the window 1915–20. The spread is small; all of them put the form in the same wartime decade, when powered flight had just become a military fact and English needed a short name for the ground that served it.
Surface analysis is straightforward: air plus the combining form -drome. That analysis and the “alteration of aerodrome” account are the same fact seen two ways. Aero- and air are historically the same word in different dress. American English simply preferred the native-looking half, the same preference that later favored airplane over aeroplane. The landing-ground pair follows the same split: learned aero- on one side of the Atlantic, vernacular air on the other, with the Greek-derived suffix held in common.
Aerodrome itself was already in English in the place sense before the American respelling. Around 1902, writers used it for a hangar that housed airships. By 1909 the same word covered the whole establishment: the field, the sheds, the equipment. An older word for a commercial flying ground would soon be airport, built on the maritime image of a port; aerodrome, and then airdrome, kept a different image, that of a course.
The racecourse suffix
The model was hippodrome, the racecourse for horses. English had had that word since the sixteenth century, from French and Latin, ultimately from Greek hippos, horse, plus dromos, a running, a race, or the track on which the race was run. When aviation needed a name for a large purpose-built ground, speakers grafted aero- onto the same ending. An aerodrome, and later an airdrome, is a course for aircraft by the same morphological joke that made a velodrome a course for bicycles and a motordrome a course for cars.
The suffix is not a folk tale invented for airplanes. Greek dromos is the same piece that English keeps in dromedary, the camel named for running, and in palindrome, a text that runs back the way it came. Syndrome, a running-together of symptoms, is another distant relative. None of these words is about flight. They show that -drome entered English as a general “course” element long before anyone needed a name for a runway.
Air, the first half of the American form, is the ordinary English noun. It reached Middle English from Old French air, from Latin aer, from Greek aēr, a word that in early Greek often meant mist or haze and later the atmosphere. Aero- is that Greek noun in combining-form shape, used in the twentieth century for gases and for aviation. Swapping aero- for air did not change the etymology. It only made the compound look like English rather than like a learned hybrid.
Two lives of aerodrome
The American spelling inherits only the place sense. The parent word had another life that airdrome never really shared.
In the 1890s the American physicist Samuel Pierpont Langley, then secretary of the Smithsonian Institution, used Aerodrome as a name for a flying machine, not a field. He took it from Greek aerodromos, an air-runner, and from a related verb meaning to traverse the air. His own later memoir dates the coinage to 1893; other references scatter it across the early 1890s, and one standard etymological notice even puts an early flying-machine use at 1891. The exact year is not settled. What is settled is the sense: Langley meant the craft itself.
The machines were tandem-wing models, steam- and later gasoline-powered, launched by catapult from a houseboat on the Potomac. Number 5 flew about half a mile in 1896. The manned full-scale versions failed in 1903, days before the Wrights flew at Kitty Hawk, and the flying-machine sense faded with the project. By the time airdrome appears in American print, English had already shifted aerodrome onto the hangar and then onto the field. The American form arrives too late to mean an air-runner. It means the ground.
Sources therefore disagree in a useful way. One line of dictionaries simply writes air plus -drome, 1915–20. Another writes alteration of aerodrome, 1917. Both are right about the American word. They are incomplete if they are read as if Langley’s machine-name were the direct parent of airdrome. The machine-name belongs to aerodrome’s first life. The landing ground belongs to its second. Airdrome is a respelling of the second.
What the American form kept, and what it lost
After 1919, airport spread as the usual United States name for a civil terminal with scheduled traffic. Airdrome was left as a synonym with a military or slightly old-fashioned colour. British and international English kept aerodrome as a general word for an airfield, sometimes specifically a smaller field as against a commercial airport. Aviation regulation still uses aerodrome as a term of art for any defined area of land or water used for aircraft operations, with or without a passenger building. That legal sense never attached as firmly to the American spelling.
The concrete residue is the suffix. Hippodrome named a course for horses. Airdrome named a course for aircraft after American English had already replaced Greek aero- with air. The flying-machine sense of the parent word dropped out; the racetrack morphology stayed on the ground.