Which Oxford reference work employed J.R.R. Tolkien after World War I?

The Oxford English Dictionary employed J.R.R. Tolkien after World War I. He worked on the dictionary from January 1919 until about mid-1920, as an assistant lexicographer in Oxford.

Tolkien helped with words beginning mainly with the letter W, researching their histories, forms, and meanings. The job gave him practical experience in historical philology, the study of how languages develop over time. That expertise later informed both his academic career and his invented languages.

A common misconception is that Tolkien wrote the Oxford English Dictionary. He did not; the dictionary was a large collaborative project developed over many decades. His contribution was a relatively brief but formative period of editorial research before he returned to academic teaching and scholarship.