Vocabulary.com: The world’s fastest, smartest dictionary: start typing a word and you’ll see the definition.
Glosbe – the multilingual online dictionary: provides free dictionaries for almost every existing language and translation memory with 1 013 284 995 sentences included.
Lexicool.com: online bilingual and multilingual dictionaries, and a directory of 7500 dictionaries and glossaries.
Proz.Com term search: Searchable glossaries in many languages pairs and domains created by a network of translators.
OneLook Dictionary: Dictionary search that allows you to find definitions and translations in various dictionaries. The website can also serve as a reverse dictionary.
Wordnik: Dictionary search that provides you with definitions from various sources, contexts, etymologies, related words and reverse dictionary function among others.
The Free Dictionary: Collection of dictionaries by subject including medical and legal together with free and subscription encyclopedias, in ten languages.
Memidex: free online dictionary and thesaurus with a simple interface, complete inflections, auto-suggest, adult-filtering, frequent updates, a browsable index, support for mobile devices, and millions of external reference links for definitions, audio, and etymology.
Etymonline.com: a map of the wheel-ruts of modern English