What reference work did J.R.R. Tolkien help edit early in his career?

J.R.R. Tolkien helped edit the Oxford English Dictionary early in his career. After returning from military service, he worked on the dictionary project from January 1919 until 1920, contributing to the history and analysis of English words.

The Oxford English Dictionary, commonly called the OED, is a historical dictionary that records meanings, usage, spelling, and changes over time through dated quotations. Tolkien worked on words beginning with the letter W, including vocabulary connected with waggle, wag, and related forms.

This employment drew on Tolkien’s training in philology, the historical study of language. It also gave him practical experience in tracing how words developed, a habit visible in the elaborate linguistic histories of Middle-earth.

The OED work is sometimes exaggerated into a claim that Tolkien wrote the whole dictionary or served as its chief editor. He did neither. His role was that of a junior lexicographer and assistant on a much larger scholarly project.