■オンライン英英辞典(主に学習者向け)
Oxford Advanced Learner's Dictionary (OALD)
http://www.oxfordadvancedlearnersdictionary.com/
Longman Dictionary of Contemporary English Online (LDOCE)
http://www.ldoceonline.com/
Cambridge Dictionaries Online (CALD,CLD)
http://dictionary.cambridge.org/
myCOBUILD.com (COBUILD)
http://www.mycobuild.com/free-search.aspx
English Cobuild dictionary (COBUILD 4版)
http://dictionary.reverso.net/english-cobuild/
Macmillan Dictionary (MED)
http://www.macmillandictionary.com/
Merriam-Webster's LearnersDictionary.com (MWALD)
http://www.learnersdictionary.com/
Merriam-Webster's Word Central (MWSD)
http://www.wordcentral.com/
Heinle's Newbury House Dictionary of American English
http://nhd.heinle.com/home.aspx
Wordsmyth
http://www.wordsmyth.net/