The OED establishes linguistic histories by citing a word's appearances in literature and popular press over time, tracing derivations from other languages, and tracing the evolution, and extinction, of words and meanings. After his return from World War I, the future novelist found himself working under founding co-editor Henry Bradley, laboring away on words like walnut, walrus, and wampum, which "seem to have been assigned to Tolkien because of their particularly difficult etymologies," notes the OED blog. These entries would later be singled out by Bradley as "containing 'etymological facts or suggestion not given in other dictionaries.'"