Admin sets KEYWORD on list. (Option for assigned mods too)
If that keyword appears in content or title anywhere a tiny icon appears next to it. This is a link to a Page where the word is defined/ decribed.
A Glossary page has a link to a meta Glossary Page listing all words in Glossary A-Z in columns.
A keyword would need to use a search system so that it covered its root and associated words. So TALKING, TALKED, TALKS would also trigger the Glossary link for TALK.