Avada Kedavra

Avada Kedavra is an ancient Arabic charm, to supposedly cause instant death.

From the Arabic for let the things be destroyed, it originated the term Abra Kadabra. In common language, the word kedavra has evolved into cedaverm, meaning dead body.

In Harry Potter and the Philosopher's Stone (American Harry Potter and the Sorceror's Stone), Voldemort used this curse to kill Harry's parents. In Harry Potter and the Goblet of Fire, Voldemort used it to kill Cedric Diggory.