GoldenDict

A feature-rich dictionary lookup program, supporting multiple dictionary formats (StarDict/Babylon/Lingvo/Dictd) and online dictionaries, featuring perfect article rendering with the complete markup, illustrations and other content retained, and allowing you to type in words without any accents or correct case.

goldendict.org

As someone who's vocabulary is limited, golden dictionary has been a life saver for my work and class work. Even if the query can't find a definition it will surely find a Wikipedia link.