ash.matadeen

This plugin provides a glossary custom post type for you to define your glossary items. Defined terms are then displayed inline on the front end.

Simple WP Glossary

Automatically adds inline definitions for user defined glossary items.

gunebakan

Free Dictionary Sidebar Widget for WordPress provides an English Dictionary that gives you English definitions, synonyms, pronunciation, spelling and more.
Visit http://www.freedictionary.org/external/wordpress/ for more information.

Free Dictionary

Free Dictionary Widget for WordPress provides an English Dictionary that gives you English definitions, synonyms, pronunciation, spelling and more.

Simple WP Glossary vs Free Dictionary