1. A male hawk; especially, male peregrine or gyrfalcon.
2. Etymology: "male falcon"; from Old French tercel (c.1200), from Middle Latin tertiolus, from Latin tertius, "third".

There are various theories as to why it is called this; one says it's because the males are a third smaller than the females; another because a third egg in the nest (smaller than the other two) is believed always to produce a male bird.