Resources

Dictionaries
Oxford English Dictionary REF PE1625 .o87 1989
Oxford English Dictionary Online
The Random House Dictionary Of the English Language, 2nd edition. REF PE1625 .R3 1987
The New Partridge Dictionary of Slang and Unconventional English REF PE3721 .P3 2006
Urban Dictionary
The Century Dictionary: An Encyclopedic Lexicon of the English Language. Folio PE1625 .C4 1889a (online version)
Webster’s Third New International Dictionary of the English Language Unabridged REF PE1625 .W36 1986 (online)
The American Heritage Dictionary REF PE1625 .A54 1982
Dictionary of American Regional English REF PE2843 .D52 1985
Word Web Online
Dictionary of American Regional English  REF PE 2843 D52 1985
Deutsches Wörterbuch  REF PF 3625 G72
Middle English Dictionary  REF PE 679 M54

Word-of-the-day sites
Merriam-Webster
Dictionary.com
Factor Words!
Monsieur Dictionnaire

Non-English-language Dictionaries
Dictionnaire Alphabétique et Analogique de la Langue Française / de Paul Robert.  REF PC2625 .R554 1985

Books about Language
Leo Rosten,  The Joys of Yiddish (1968) PN6231.J5 R67