Surefire describes something that cannot fail. A surefire way to fall asleep is one that works every time. A surefire hit is a song or film everyone is certain will succeed.

It goes in front of a noun, and it goes in front of a small family of nouns in particular: a surefire way, a surefire method, a surefire hit, a surefire winner, a surefire success. You will rarely see it anywhere else, so it is best learned as part of those phrases rather than as a loose adjective.

The tone is casual and cheerful — advertising, magazines, friends giving advice. "Here are five surefire ways to save money." And notice what that tone does: because the claim is so absolute, it is often used a little loosely, or with a wink. When a newspaper calls a young player a "surefire star," everyone knows nothing in life is truly certain; the word is enthusiasm, not a guarantee. It also turns up in the phrase "a surefire bet," which people say about things that then sometimes lose.

The spelling varies: surefire, sure-fire, and sure fire all appear. Surefire and sure-fire are both common and safe. The origin is from guns — an old sure-fire weapon was one that always went off when you pulled the trigger, never a misfire — which is a nice picture to keep in your head.