It's a bird, it's a plane, it's...

For non-Chinese readers:
The second and third chinese characters, 鸡 and 机 (ji) have the same pronunciation.
飞机 (fei ji) literally means 'flying (fei) machine (ji)', i.e. aeroplane.
飞鸡 (fei ji) literally means 'flying (fei) chicken (ji)'.