Google Dictionary is another great resource from Google.
Like most dictionaries, it returns the word, in phonetic spelling, with an audio file on how to pronounce it. There is also the definitions, related phrases, related languages, usage examples and web definitions. The related language shows if the same word exists in another language.
The related phrases and usage examples are great for trying to truly understand a word and how it is used. This is a great tool for all teachers and students.
Here is what was returned for "teacher":
