To latch means to fasten or lock something using a simple catching device. When you latch a gate, you flip a small metal bar or hook that holds it closed. Many doors have latches that click into place when you shut them, keeping the door from swinging open. Unlike a key-operated lock, a latch is usually a simple mechanical device you can open and close quickly from either side.

A latch is also the fastening device itself: the hook, bar, or catch that holds things together. An old wooden chest might have a metal latch on the front, or a barn door might close with a heavy sliding latch.

You might hear someone say they latched onto an idea, meaning they grabbed it eagerly and won't let go. If you latch onto a new hobby like building model rockets, you become deeply interested and focused on it. When a younger sibling latches onto you at a family gathering, they stick close by your side and follow you around.

The phrase latchkey kid describes a child who comes home to an empty house after school and uses their own key to let themselves in, though this term is somewhat old-fashioned now.