Lockpin

Part of speech: noun

Definitions

1. A small device used to secure a lock by preventing its parts from moving ; a part within a lock mechanism that holds or releases other components to lock or unlock
2. A device designed to keep a lock closed by blocking movement in the locking system ; an internal piece that interacts with pins or tumblers to maintain a lock’s security
3. An element inserted to restrict a lock’s operation and enhance security ; a mechanical part that engages within a locking mechanism to control access

Etymology: A lockpin is about as transparent as compounds get: it is simply a "lock" joined to a "pin," the two English words combined. The pin in question is the small peg-like part that the mechanism depends on, and the lock is the fastening it governs, so the name describes the object directly rather than through metaphor. Locks have used pins of this kind for centuries, most familiarly in the pin tumbler design, where spring-loaded pins must be lifted to exact heights before the mechanism will turn. The word is also used in a second sense, for the component inside a lock that holds or releases other parts, which follows the same logic. Because the term is a plain combination of two common words, its meaning is recoverable from its parts, and the history offers few surprises beyond that.