Headfirst means moving or diving with your head going before the rest of your body. When a swimmer dives headfirst into a pool, their head enters the water first, followed by their arms, torso, and legs. When a baseball player slides headfirst into second base, they launch themselves forward with their head leading the way toward the bag.

The word also describes rushing into something without thinking it through. When someone jumps headfirst into a new hobby, they throw themselves into it with total enthusiasm, maybe buying all the equipment before they even know if they'll enjoy it. A student who plunges headfirst into a difficult project without planning might find themselves confused and overwhelmed.

This second meaning captures how literal headfirst motion can feel risky: your head is vulnerable, and you can't see everything that's coming. Going headfirst into any situation means committing completely and immediately. Whether that's brave, reckless, or just wonderfully enthusiastic depends entirely on the situation.