Sentence:  Wikipedia has a well-known policy (to experienced editors, at least) stating what kinds of information belong in the encyclopedia. The sister projects that the Wikimedia Foundation supports, such as <WSD>Wiktionary</WSD>, fulfill some of the roles that Wikipedia does not. ... <WSD>Wiktionary</WSD> is a free, multilingual dictionary with definitions, etymologies, pronunciations, sample quotations, synonyms, antonyms and translations. It's the "lexical companion" to Wikipedia. 
Meaning of the word marked with <WSD> tags:  A collaborative project run by the Wikimedia Foundation to produce a free and complete dictionary in every language; the dictionaries, collectively, produced by that project.