You can find many dictionaries in the ESL collection. Below are some of the available titles.
Longman English Dictionary Online
Longman English Dictionary is the leading dictionary for learners of English of all ages and levels who want to learn more about English.
Merriam-Webster's learners Dictionary for ESL
This dictionary of American English, which includes practice exercises, is great for ESL students.
Merriam-Webster Online Dictionary
This dictionary will guess at the word you need, even if you cannot spell it exactly right.
Merriam-Webster Visual Dictionary Online
This dictionary has pictures to help explain words.
The Library has dictionaries for the following languages: Spanish, Polish, French, German, Chinese, Urdu, Hebrew, Arabic, Korean, Farsi, Portuguese, and Albanian.
Lexipedia is an online dictionary and thesaurus. Lexipedia presents words with their semantic relationships displayed in an animated visual word web. Lexipedia supports English, Dutch, French, German, Italian, Spanish languages.