In 1945 he succeeded R. W. Chambers as honorary director of the Early English Text Society and worked to extend its publishing program.
He was editor of Medium Aevum, the journal of the Society for the Study of Medieval Languages and Literature, from its inception in 1932 to 1956.
Onions' last twenty years were largely devoted to completing The Oxford Dictionary of English Etymology (1966), which treated over 38,000 words and went to press just prior to his death.
During World War I, Onions served in British naval intelligence where his knowledge of German proved a significant asset.
[1][5] Anne Onions, one of his daughters, worked for many years in the Earth Sciences department at the University of Oxford as the departmental secretary and financial administrator.