These volumes replace the 1933 Supplement to the OED. The vocabulary treated is that which came into use during the publication of the successive sections of the main Dictionary -- that is, between 1884, when the first fascicle of the letter A was published, and 1928, when the final section of the Dictionary appeared -- together with accessions to the English language in Britain and abroad from 1928 to the present day. Nearly all the material in the 1933 Supplement has been retained here, though in revised form (Preface).
