The Oxford Companion to Chaucer. Ed. Douglas Gray. NY: Oxford University Press, 2003. Short to medium-length articles on topics and allusions about or within Chaucer's works, life, and historical context.
The Oxford Dictionary of the Middle Ages. Ed. Robert E. Bjork. NY: Oxford University Press, 2010. Covers all key aspects of European history, society, and culture from 500 to 1500 A.D., as well as the Byzantine Empire, Islamic dynasties, and Asiatic peoples of the era. It is designed both for medievalists, who need a detailed and reliable reference tool, and for students and general readers seeking an accessible guide to the period.
Dictionary of the Middle Ages. Joseph R. Strayer, editor-in-chief. NY: Scribners, 1982-1989. 13 vols.+ Supplement (2004). Geisel 5th Fl. D114 .D5 1982.
Lexikon des Mittelalters. Munchen & Zurich: Lexma, 1977-1999. 10 volumes. Geisel 5th Fl. D101.5 .L49. For those who read German, this is another comprehensive scholarly encyclopedia of history, culture, and literature of the Middle Ages in Europe and parts of North Africa and the Middle East.
The New Arthurian Encyclopedia. Ed. Norris J. Lacy. Updated paperback edition. NY: Garland, 1996. Geisel 5th Fl. DA 152.5 .A7 N48 1996.
Bosworth, Joseph. An Anglo-Saxon Dictionary. Edited and enlarged by T. Northcote Toller. London: Oxford University Press, 1954. (First published 1882-1898.) Supplement, by T. Northcote Toller. London: Oxford University Press, 1955. (First published 1908-1921. Still the most complete Anglo-Saxon dictionary currently available. Geisel 7th Fl. PE 279 .B5 1954 / supplement.
Clark, John R. Clark. A Concise Anglo-Saxon Dictionary. 4th ed. Cambridge: Cambridge University Press, 1960. Geisel 7th Fl. PE 279 .H3 1960.
Edmonds, Flora, Christian Kay, Jane Roberts, and Irene Wotherspoon. A Thesaurus of Old English. University of Glasgow Online. The printed volumes, by Roberts and Kay (Amsterdam: Rodopi, 2000, 2 volumes) are on Geisel 7th Fl. PE 279 .R62 2000.
Dictionary of Old English. The Dictionary of Old English (DOE) defines the vocabulary of the first six centuries (C.E. 600-1150) of the English language, using twenty-first century technology. The DOE complements the Middle English Dictionary (which covers the period C.E. 1100-1500) and the Oxford English Dictionary, the three together providing a full description of the vocabulary of English. NOT CURRENTLY AVAILABLE AT UC San Diego. Please examine the website and let me know if there is interest.
Middle English Dictionary (MED). Ed. Hans Kurath et al. Ann Arbor: University of Michigan Press, 1952-2001. 13 volumes. Its 15,000 pages offer a comprehensive analysis of lexicon and usage for the period 1100-1500, based on the analysis of a collection of over three million citation slips, the largest collection of this kind available. Available on line through The Middle English Compendium, which preserves all the details of the print MED, but goes far beyond this, by converting its contents into an enormous database, searchable in ways impossible within any print dictionary. UC San Diego's print set is at SRLF.