From this page you can search any one of five Cambridge online dictionaries; International English, the Learner's Dictionary, American English, Idioms and Phrasal Verbs. The search returns a comprehensive list of meanings as well as occurrences in common phrases and idioms. The site also features a small selection of online activities to practise phrasal verbs, idioms and general vocabulary.

Previously a free online resource, Harper Collins have now decided to make some money out of it and it is presently only available on CD-ROM or DVD.

Longman now allow developers to integrate the web dictionary into educational web sites. You need to apply to Longman for permission, and, if successful, they will send you a piece of source code to insert into your web pages. This will allow users to double click on any word and bring up the definition in a pop up window. A useful resource for centres creating online activities or materials and who don't want to develop a dictionary or glossary from scratch.

If you need ideas for teaching dictionary skills, this is a useful site. The most recent e-lessons and teacher's notes are archived for you to download and print whenever and wherever it suits you. Initial e-lessons are for use with Macmillan dictionaries in particular but more recent e-lessons can be used with any dictionary.

Heinle & Heinle's Newbury House Online Dictionary is based on the Newbury House Dictionary of American English and contains around 40,000 entries. The resource is free. A Cultural Note of the Day explains idioms.

The online version of the twenty-volume second edition (1989) of the OED is available only on an annual subscription basis. Individual and network licences are available. The site offers a free 'Word of the day'.

This uses special software to display linked words from an online thesaurus (WordNet at Princeton University). It is a great vocabulary development resource for very high-level students (and teachers). You can focus the map on different parts of speech. The software could help students with the idea of mindmaps for recording words in groups according to their meaning.

Lycos' RhymeZone is a dictionary/thesaurus that searches by keyword for rhymes, synonyms, antonyms, related words, similar sounding words, homophones, etc, as well as simple definitions, although here these take second place. It also searches for your keyword in the complete works of Shakespeare and in a wide range of quotations from famous people.

WordNet, from Princeton University, is concerned with organizing words in synonym sets and with the relation between these sets. An initial search for meanings can then be refined into searches for synonyms, hypernyms, hyponyms, holonyms and meronyms.

Wordsmyth is an online dictionary of American English that combines dictionary and thesaurus. It contains around 50,000 headwords. Your search term is returned with all definitions, each cross-referenced to synonyms, similar and related words. Potentially useful for developing writing skills.