Automatic Synonyms (Google Weblog)
Google is now using synonyms automatically on difficult searches. For example, when you search cooking octopus teacher cartoon it notes “By default, Google searches for variations of your search terms.” and returns results with the word “teaching”, not just “teacher”.
This is a variant of something known more precisely as “stemming” where the parser breaks “teaching” to its stem word “teach.” Coming up with variations is not as difficult as stemming is in the first place.