Displaying Definitions in Context

Providing definitions in context is helpful, particularly for technical terms users may not understand. This page on meningitis uses a dotted underline to differentiate definition pop-ups from links that go to a different page (which use a solid blue underline line):

This site for human resource professionals also provides definitions, but it uses text color to differentiate definitions vs. links—orange for definitions and blue for links. This approach can cause problems for color-blind users.

There are also less obtrusive implementations. The New York Times displays a button for definition look-up when a user selects a word. This is appropriate for a more generalized definition function, which in case of the New York Times is linked to the American Heritage Dictionary.