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

J.R.R. Tolkien helped compile The Oxford English Dictionary early in his career.

After serving in the First World War, Tolkien worked on the staff of the Oxford English Dictionary from January 1919 until 1920. He contributed to the history and development of words beginning with the letter W, including research into their origins and forms.

The dictionary project was a vast historical undertaking. Its editors traced words through dated quotations, showing how meanings and spellings changed over time. Tolkien’s training in philology made this work a natural fit, and the experience deepened his understanding of Germanic languages.

Tolkien did not create the entire dictionary, and his later fame as a novelist can obscure this scholarly employment. His dictionary work belongs to the period before his university teaching career and before The Hobbit was published.