onǣlan

Old English onǣlan meant to set on fire, to kindle—from on (on) and ǣlan (to burn). The word described starting a fire, nothing more. But somewhere between Old English and Middle English, metalworkers adopted the word for a specialized process: heating metal to a specific temperature and then cooling it slowly, relieving internal stresses and making it softer.

The shift in meaning is remarkable. A word that meant to set ablaze came to mean to heat with precise control. The metalworker's anneal is the opposite of quenching (rapid cooling, which makes metal hard and brittle). Annealing is patience applied through heat—bringing a material to its transformation temperature and then letting it cool at its own pace.

By the seventeenth century, anneal had expanded to glassmaking. Glass that cools too quickly develops internal stresses and shatters easily. Annealing glass—holding it at a controlled temperature, then cooling it gradually—produces durable, stable material. The windows in medieval cathedrals survived centuries because glassmakers understood annealing.

Simulated annealing, a computational optimization technique invented in 1983 by Scott Kirkpatrick, C. Daniel Gelatt, and Mario Vecchi, uses the metallurgical metaphor: the algorithm starts with high randomness (heat) and gradually reduces it (cooling), allowing a system to find optimal configurations. The Old English word for fire now helps computers solve problems.