Manual:$wgActionPaths

Details
To set 'pretty' URL paths for actions other than plain page views, add to this array. For instance: There must be an appropriate script or rewrite rule in place to handle these URLs.

Rewrite rules
This option needs an appropriate rewrite rule to work.

To rewrite most actions to a specific path, one could make the following changes to LocalSettings.php:

In Apache, code a rewrite rule similar to the following:

This will forward all requests to /action/actionword/title to index.php?action=actionword&title=''title.

Spam prevention
Using $wgActionPaths, especially for the edit action seems to reduce the number of spam bots attempting article edits. It is suspected that bots are programmed to look for action=edit to identify a MediaWiki installation and act appropriately. With this in mind, it would be beneficial to name your action prefix something non-apparent so bots can't find your site when they start looking for action/edit.