Onions, Charles Talbut (1873–1965), lexicographer and grammarian, was born at 40 Spring Street, Edgbaston, Birmingham, on 10 September 1873, the eldest son of Ralph John Onions and his wife, Harriet, daughter of John Talbut, locksmith. Although the traditional occupation of the family had been bellows making, his father was a designer and embosser in metal; the name is of Welsh origin, being based on the form Einion. Charles Talbut Onions was grounded in grammar, first at a board school and later at the Camp Hill branch of King Edward VI's foundation at Birmingham. There he came under the influence of the Revd A. J. Smith, a headmaster of sterling character and scholarly outlook, to whom he owed the very means of entering academic life as well as his first contact with lexicography: Smith kept Littré's French dictionary in his classroom, together with fascicules of the New English Dictionary as they appeared. At school, too, Onions was much influenced by a Tractarian organist and choirmaster, John Heywood: his religious sympathies and affiliations were thus permanently established.

With a leaving exhibition Onions entered Mason College, Birmingham, where he studied for the London BA degree, which he gained in 1892 with third-class honours in French, followed in 1895 by his MA degree. Under E. A. Sonnenschein he learned inter alia to scan Plautus and to write Greek prose, and he contributed An Advanced English Syntax (1904; frequently reprinted) to a Parallel Grammar Series published by Sonnenschein. The professor of English at Birmingham at this time was Edward Arber, who introduced Onions to J. A. H. Murray when the latter was examining at Birmingham in the Oxford local examinations. Shortly after, in September 1895, Murray invited Onions to join the small staff of the English dictionary at Oxford, and at Oxford he lived, except for one short interval, for the rest of his life. There he was soon joined by Henry Bradley; in later years he spoke of passing from Murray to Bradley as a remarkable experience: 'It was to pass from the practical, professional teacher to the philosophical exponent.' On 17 April 1907 he married Angela (1883/4–1941), youngest daughter of the Revd Arthur Blythman, rector of Shenington; they had seven sons and three daughters.

From 1906 to 1913 Onions was entrusted with the special preparation of various portions of the dictionary under the supervision of Bradley and W. A. Craigie, and then began independent editorial work on the section Su–Sz; he was also responsible for Wh–Worling and the volumes containing X, Y, and Z, and so contributed the very last entry to the whole work in the form of a cross-reference—'Zyxt, obs. (Kentish) 2nd sing. ind. pres. of See v.'—which he liked to mention as it was taken, because of its position, as a brand name for a soap. But it was by no means Onions's last word.

In 1922, after the death of William Little, the Clarendon Press commissioned Onions to revise and complete Little's work on the Shorter Oxford English Dictionary. This appeared in 1933, and was continually revised and augmented by him until 1959: in the twenty pages of addenda in the 1944 edition he dealt with 1500 words, mostly the product of war. Onions shared with Craigie the preparation of the supplement to the main work (1933), which includes a list of books cited therein that constituted the fullest bibliography of English literature yet made. An equally valuable by-product was his Shakespeare Glossary (1911), the introduction to which provides a notable survey of Shakespearian usage; throughout the work he was able to draw on his knowledge of the Warwickshire dialect. On the death of Sir Sidney Lee he completed the editing of Shakespeare's England (1916), contributing to the articles on alchemy and on animals, as well as providing a glossary of musical terms. Henceforth the Clarendon Press constantly called on him for advice and help, and many Oxford books owe improvements to him. For many years he was the only visitor allowed into the Walton Street office at 'the sacred hour of 9.30' when the day's work was being planned. The files of the press are rich in his scholarly jottings.

In 1918 Onions donned uniform and went to the naval intelligence division of the Admiralty (where his knowledge of German was put to good use) with the rank of honorary captain, Royal Marines. On his return to Oxford he became university lecturer in English (1920) and later reader in English philology (1927–49). In 1922 he revised for the Clarendon Press the Anglo-Saxon Reader originally compiled by Henry Sweet, though 'reverence for the opinion of a great master' restrained the correcting hand. On Bradley's death in 1923 Magdalen elected Onions to fill the vacant fellowship; when the statutes were revised shortly afterwards he chose to remain under the old regulations, and so remained a stipendiary fellow until the day of his death. In 1940–55 he was librarian of the college, and undergraduates and others profited from his constant presence in the dictionary bay of the library; he was equally at home in the senior common room, where his astringent rejoinders to questions on etymology and English usage were much relished.

Onions was president of the Philological Society from 1929 to 1933, and was elected FBA in 1938. Oxford, Leeds, and Birmingham conferred honorary degrees upon him on the completion of the dictionary, and he was appointed CBE in 1934. In 1945 he succeeded R. W. Chambers as honorary director of the Early English Text Society, and, partly by enlisting the help of several former pupils at Oxford, he did much in the following twelve years to extend its publishing programme. 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. But the preoccupation of his last twenty years was the Oxford Dictionary of English Etymology (1966), which went to press before he died. It treats over 38,000 words and is likely to be his enduring monument.

Onions had an almost personal pride in his mother tongue, which he once described as 'a rum go—but jolly good'. His lifelong study of it bore fruit in the masterly chapter on the English language which he contributed to The Character of England (1947), edited by Sir Ernest Barker. His training in the scriptorium of the dictionary taught him the art of conciseness, as is demonstrated in his tracts for the Society for Pure English and in his article 'Grammar' in Chambers's cyclopaedia. As a lexicographer his strength lay in etymology: he delighted in teasing out the history of such words as ‘syllabus’ or ‘acne’ or Shakespeare's 'dildos and fadings'. His grasp of idiom and his analytical power are well evidenced in the articles in the Oxford English Dictionary on 'set', 'shall', 'will', and the interrogative pronouns. To dialectal usages, medieval and modern, he was particularly sensitive. His approach to linguistic and lexical problems was essentially pragmatic. There was something Johnsonian in his attitudes and character (as well as his early struggles). For much of his life he was handicapped by a stammer and he always had a fellow feeling for other stammerers; but he was undemonstrative in his likings as in his religion. He died at the Radcliffe Infirmary, Oxford, on 8 January 1965, and was buried on 13 January.