Did you know that many online dictionaries have much more than just words and definitions? Check out some of these links for lots of great activities like spelling games, crosswords, word origins and special features!
1) Dictionary.com - this site has the most dictionary activities. Check out Word Dynamo (http://dynamo.dictionary.com/) where you can test how many words you know, as well as practise with lessons on lots of topics. Or you can try word games like these - http://dictionary.reference.com/fun
2) Oxford Dictionaries - you can find lots of great stuff here too like their spelling bee (http://bit.ly/or0QHh), Hangman (http://bit.ly/tMsYo7) and more difficult crosswords (http://bit.ly/vBywUD)
3) Cambridge Dictionaries - this site has a great blog that looks at new words every week which you can't find in regular dictionaries. It's great!http://dictionaryblog.cambridge.org/about-new-words/
4) MacMillan Dictionary - this dictionary is unique in having sound effect buttons! Do you ever have trouble imagining what words like moan, groan, whine etc. really mean? Well with MacMillan you don't have to - you can hear for yourself! Just click the little musical note button! http://www.macmillandictionary.com/dictionary/british/moan