Ding is a dictionary lookup program for the X Window system on Linux/Unix. It comes with a German-English Dictionary with about 253,000 entries. It is based on Tk version >= 8.3 and uses the agrep or egrep tools for searching. In addition ding can also search in English dictionaries using dict(1) and check spelling using ispell(1). It has many configuration options, such as search preferences, interface language (English or German), and colors. It has history and help functions and comes with useful key and mouse bindings for quick and easy lookups.
Artha is a handy thesaurus based on WordNet with distinct features like global hot key look up, passive desktop notification, regular expression based search, etc. Artha may be used as a free open-source replacement/clone to the proprietary WordWeb Pro thesaurus (which is also based on WordNet) on Unix-like and Windows operating systems.
new-words is a script that helps you to control your vocabulary and find unknown words in texts before you start to read them. It is intended to be run in a console; the interactive part of the work is done by means of a text editor (vim by default). It features: words frequency information about words in a text; users vocabulary control; support for several languages; dictionary software integration; and the ability to make notes for unknown words.