Yahoo! Education Reference
"Yahoo! Education offers a handy selection of searchable reference materials to help you find the information you need.
Look up the definition of a word in the Dictionary, find its synonym in the Thesaurus, or translate it into Spanish.
Search for facts and information in the Encyclopedia, find country and regional maps and flags in the World Factbook, and much more."
The reference tools listed on the page includes:
The American Heritage® Dictionary, Fourth Edition
The American Heritage® Spanish Dictionary, Second Edition
Roget's II: The New Thesaurus
Columbia World of Quotations