StarDict
How did not I pay attention to that during all this time? An only-1-MB GTK-based offline dictionary!
StarDict is a Cross-Platform and international dictionary written in Gtk2 and data is availbale from the Website. I started to find out about it downloading both Oxford Advanced Learner’s Dictionary and the Russian Словарь Даля. Those data files are enough complete as they contain words from different fields: computing, literature, … and even slangs!
Another cool feature, while the software is running, you can get the definition of any word from any external program (Firefox for example) just by selecting it.
Installation is not difficult at all: you may download an RPM package or a tarball file that you uncompress and compile with any recent GCC version, you also have to copy data files to your share directory, for example /usr/local/share/stardict/dic/
Did I finally mention it’s Free? 
