For a substantial portion of its flight, a spacecraft is an aircraft. A first stage like the Super Heavy doesn't even necessarily exit the atmosphere. Super-Heavy's intended MECO & stage separation is 65km, well below the accepted 100km "edge of space" definition. Super-Heavy is an aircraft, Starship is both an aircraft and a spacecraft.

Not only is a spacecraft an aircraft under US federal law, a hypothetical quadcopter the size of a beetle is an aircraft under it as well.

Anything that flies through the air, not under a roof, using active control is an "aircraft".