Yes — but note that this is an experimental feature (v0.7 and higher) and may not always work correctly!
The tilde prefix (~) can be used to restrict blocking to sites that contain given keywords. Within a keyword you can use an asterisk (*) to match any number of characters (except whitespace) and an underscore (_) to match whitespace. Note that the keyword matching is not case-sensitive.
So, for example, you could enter the following into the list of sites:
This would result in pages on the sites somesite.com and anothersite.com being blocked only when those pages contain the complete word “anteaters” or any word beginning with “crypto” or any word ending with “alicious” or the complete phrase “green eggs and ham”.
If you want to block pages on any website that contain given keywords, you’ll need to use wildcards to specify all websites. For example: