Synonyms dictionaries are useful resources for natural language processing. Unfortunately their availability in digital format is limited, as publishing companies do not release their dictionaries in open digital formats. Dicionário-Aberto (Simões and Farinha, 2010) is an open and free digital synonyms dictionary for the Portuguese language. It is under public domain and in textual digital format, which makes it usable for any task. Synonyms dictionaries are commonly used for the extraction of relations between words, the construction of complex structures like ontologies or thesaurus (comparable to WordNet (Miller et al., 1990)), or just the extraction of lists of words of specific type. This article will present Dicionário-Aberto, discussing how it was created, its main characteristics, the type of information present on it and the formats in which it is available. Follows the description of an API designed specifically to help Dicionário-Aberto processing without the need to tackle with the dictionary format. Finally, we will analyze the results on some data extraction experiments, extracting lists of words from a specific class, and extracting relationships between words.