Personally, If I needed to use an operator other than a hyphen '-' I would use an underscore because it seems cleaner and is often used for variables when writing code.
In your comments you said you're needing the extra operator to perform a search using the words in the URL. If this is the case I would probably use the plus '+' symbol. Many websites replace spaces with the plus symbol and so if you're aiming to parse the URL into separate words this may be easier.
The only other option I would suggest is using URL parameters like
url.com?var1=term1&var2=term2 and using a .htaccess file to convert it to a clean, readable URL like
The link below is a great article about using .htaccess files. The first point explains what I mentioned above.