To tighten means to make something more secure, firm, or close-fitting by pulling, twisting, or adjusting it. When you tighten your shoelaces, you pull them snug so your shoes won't slip off. When a mechanic tightens a bolt, she turns it until it's firmly in place and won't come loose.

The word works for both physical objects and abstract ideas. You might tighten a lid on a jar, tighten your grip on a rope during tug-of-war, or feel your stomach muscles tighten when you're nervous. A coach might tighten up the defense by having players guard more closely. A teacher might tighten the rules if students have been too rowdy at recess.

Tighten is the opposite of loosen. If you've loosened something too much, you need to tighten it back. Sometimes things need periodic tightening: bicycle chains get loose over time, guitar strings need tightening to stay in tune, and even friendships sometimes need tightening when people haven't spent time together in a while. The key idea is always the same: making something more secure, closer, or firmer than it was before.