Although the OED is the best-known historical dictionary, it is not the only one. Specialized dictionaries, some now online, examine particular chronological periods, registers, or geographical regions. Currently at the letter G, Dictionary of Old English, edited by Antonette diPaolo Healey, defines words for the period from 600 to 1150. To date, the largest complete dictionary of Old English remains that of Joseph Bosworth and T. Northcote Toller, An Anglo-Saxon Dictionary, first published in 1898 with a supplement in 1921.
The six-volume English Dialect Dictionary (EDD), edited by Joseph Wright, traces the history of dialect words in England from about 1700 to 1900. A project to digitize the EDD, with its 70,000 entries, is under way at Innsbruck University Library, and a nondigitized scan is available through the University of Toronto Library. Middle English Dictionary, edited by Hans Kurath and Sherman Kuhn, which took a half century to complete, covers the period 1100-1500, and is based on a collection of more than three million citation slips. It was released as a 15,000-page set of printed volumes, but since 2007 has also been available free in electronic format hosted by the University of Michigan.
Sir William Craigie, an OED editor, was the originator of the four-volume A Dictionary of American English on Historical Principles (DAE), which includes American English words from the settlement to the start of the twentieth century and was intended to complement the OED. The DAE was in turn one of the sources for A Dictionary of Americanisms on Historical Principles, edited by Mitford Mathews, a two-volume work tracking 50,000 words and phrases and including both American coinages (like bifocals and ivory tower) and English words that took on new American meanings (like buffalo and refrigerator).
Dictionary of American Regional English, edited by Frederick G. Cassidy and Joan Houston Hall, is based on face-to-face interviews conducted between 1965 and 1970 and supplemented by a collection of vernacular written materials from the Colonial period to the present. Published in five volumes (over a period of twenty-seven years beginning in 1985) and now available in an electronic edition, DARE includes entries on fieldwork by region (often supplemented by maps), the earliest known usage of each word, and examples showing use over time. The history of the English language is also told in its slang. Jonathon Green’s three-volume Green’s Dictionary of Slang covers the slang of the entire English-speaking world from 1500 to the present: its 53,000 headwords define 100,000 words using more than 413,000 citations. The Historical Dictionary of American Slang, edited by Jonathan Lighter, offers an OED-like tracing of etymological development through dated citations and entries with field and usage labels; however, only the first two volumes have been published, covering A-G and H-O.
Finally, there are etymological dictionaries, less concerned with usage than with origins. The Oxford Dictionary of English Etymology, edited by C. T. Onions with G. W. S. Friedrichsen and R. W. Burchfield, is a comprehensive work giving brief accounts of the origins and history of more than 38,000 words. The Barnhart Dictionary of Etymology, edited by Robert Barnhart and Sol Steinmetz, which boasts that it is based on American scholarship, gives etymologies of about 30,000 words. The difference between a slang dictionary and an etymological one can be found in entries like that of cool, which Barnhart straightforwardly explains as having developed from Old English cōl. The Historical Dictionary of American Slang, by contrast, devotes two pages to the development of the various senses of the word.
 The DARE maps are quite unusual looking in that they are based on population density as of the 1960s and the number of interviews done in each state, thus skewing size of the states while maintaining their geographical relationships.
 These two volumes were published by Random House (as the Random House Historical Dictionary of American Slang); however, in 2003 the project moved to Oxford University Press, which is publishing the two remaining volumes covering P-S and S-Z. For more on slang resources, see this author’s essay “Groping for Words: A Guide to Slang and Usage Resources,” Choice: Current Reviews for Academic Libraries 44:4 (Dec. 2008), 619-31.