On which major reference work did J.R.R. Tolkien work as an assistant lexicographer?

J.R.R. Tolkien worked as an assistant lexicographer on The Oxford English Dictionary.

After serving in the First World War, Tolkien joined the staff working on the dictionary in 1919. He was involved with words beginning with the letter W, examining historical evidence, meanings, spellings, and forms across earlier stages of English. The work gave him practical experience in tracing how words developed over time.

Tolkien’s training in philology—the historical study of language—was important to both his academic career and his creative writing. He later taught Old and Middle English at Oxford and developed constructed languages for his fictional peoples, often building them with the depth and internal history of real languages.

The dictionary was originally known as the New English Dictionary on Historical Principles. It was renamed the Oxford English Dictionary in 1933. Tolkien’s employment there was relatively brief, but it is frequently mentioned because it connects his professional linguistic skills with the language-making that became a defining feature of Middle-earth.