WordWeb is an international dictionary and word finder with more than 300 000 possible lookup words and phrases. It is also available as Windows software.
WordWeb fully covers American, British, Australian, Canadian and Asian English spellings and words. It is updated regularly, and has no annoying adverts.
If a word isn't found the search feature automatically searches other dictionaries and an encyclopedia, and shows you anything it finds. The database indexes over a million different entries. You can also cross-reference to definitions on other sites. And if you don't know a word in a definition, you can click on it to take you to its definition.