loon [L19th] This word for ‘a silly person’ comes from the North American loon [M17th], a large water bird also known as a diver. It gets its name from its distinctive cry. The sense silly is from the bird’s actions when escaping from danger; perhaps influenced by loony, a mid 19th-century abbreviation of lunatic [ME] from Latin luna ‘moon’. In the past people thought that the phases of the moon could affect people.