Abstract : Semantic lexical resources are a mainstay of various NLP applications. However, comprehensive and reliable resources rarely exist or are often not freely available. We discuss in this paper the context of lexical resources building and the problems of evaluation. We present Wiktionary, a freely available and collaboratively built multilingual dictionary and we propose a semi-automatic approach based on random walks for enriching its synonymy network, which uses endogenous and exogenous data. We then propose a validation "by crowds". Finally, we present an implementation of this system called WISIGOTH.