You can use the title attribute for definitions and footnotes which will appear when the user hovers over the text.
Select Embed from the Insert menu and choose Embed Code:
<span style="border-bottom:thin dashed green" title=" Definition for Some Text ">Some Text</span>
<span style="border-bottom:solid green" title=" Definition for Some Text ">Some Text</span
<P STYLE="font-family: Sans-Serif;font-size: medium;font-weight: bold;">This is the information site for the Shiawassee County Michigan (USA) <span style="border-bottom:solid green" title=" Digital Smart Technologies for Amateur Radio ">DSTAR</span>Amateur Radio Digital Repeater.</P>
or
Footnote<span style="color:red" title=" Footnote text ">[1]</span>
Note: Not all browsers will display the title attribute and not all screen readers will speak the text.