crimson090

Adds buttons to the Text (HTML) edit which generate Markdown syntax. These buttons serve as a great introduction to 
users who are new to Markdown, as well as shortcuts for more experienced users. The buttons include:
<ul>
<li>Bold</li>
<li>Italic</li>
<li>Blockquote</li>
<li>Link</li>
<li>Code</li>
<li>Table</li>
<li>Headers</li>
<li>Help (links to external Github Markdown guide)</li>
</ul>
This plugin does not modify the Visual editor, as that editor is not ideal for writing Markdown in. It’s recommended you disable 
the Visual editor entirely to enforce using Markdown.
Note that this plugin does not render Markdown. You should use a plugin (such as Jetpack Markdown) to render markdown in your theme.

MarkdownBar

Adds a toolbar of buttons to the Text (HTML) edit which generate Markdown syntax

LuckyWP

The plugin replaces plain-text editor for category, tag and custom taxonomy term description with the built-in WordPress WYSIWYG editor (TinyMCE). This is allow you to insert images, use shortcodes, embed videos, audio and other content into term description.
<h4>Features</h4>
<ul>
<li>Edit category and tag description with built-in WordPress WYSIWYG editor (TinyMCE).</li>
<li>Work in add and edit term forms.</li>
<li>Support WooCommerce category and tag description.</li>
<li>Support custom taxonomy term description.</li>
</ul>

LuckyWP Term Description Rich Text

Thanks to the author for the work. I already use on two sites

Very useful plugin

Replaces plain-text editor for category, tag and custom taxonomy term description with the built-in WordPress WYSIWYG editor (TinyMCE).

MarkdownBar vs LuckyWP Term Description Rich Text