Invaluable means so useful or precious that you can't put a value on it. It's one of those tricky words that means the opposite of what you might expect: something invaluable isn't worthless, it's so valuable that no price tag could capture its worth.

A firefighter's experience is invaluable when rescuing people from a burning building. A good friend's support during a difficult time is invaluable. Your grandmother's advice, earned through decades of life, might be invaluable even though you couldn't buy it in any store.

The confusion happens because “in” usually means “not,” like how “invisible” means “not visible.” But with invaluable, think of it as “impossible to value” because the thing is worth too much, not too little.

When something is invaluable, it means you'd be lost without it. A scientist's decades of research notes are invaluable to her work. A teacher's patience is invaluable to struggling students. The word recognizes that some things matter so much that trying to measure their worth in dollars misses the point entirely.