When you are producing text for your website you may well want to use synonyms within your text but may also be concerned that search engines, such as Google and Bing, will class this as a form of keyword stuffing and impose a penalty on your site for doing so or not realise that the words have a collective meeting and rank your site lower than if you had used just one word over and over again. In a recent video Matt Cutts has answered this question… well, sort of!
In the video Matt says that Google have a synonym team who look for words that have the same meaning such as “car” and “auto”. He goes on to say that as long as the words are used in a natural way then there should not be any penalty incurred. What he does not go on to say is whether these synonyms are used as signals to help you achieve higher rankings. From my own experience I would say that they do. My correct name is Michael Walmsley but some of my friends know me as Mike and others as Mick, if you search online for Michael Walmsley, Mike Walmsley or Mick Walmsley then you will see that this website is pretty near the top of the rankings no matter which version of my name that you use. Only one of the names is fully included in my domain name and I rarely use the name Mick in my business dealings or online. Yet my website ranks highly for all three versions of my name so that would suggest that Google knows that Michael, Mike and Mick are all interchangeable. If this is the case then it should also follow that by using a variety of synonyms rather than the same keyword within a document that you will gain improved rankings for your keyword. I cannot say whether using a keyword four times in a document would be preferable or not to using the keyword twice and a synonym twice.
However, Matt does say that you should create natural reading documents. This makes sense as Google is looking for high quality content and an article that does not read naturally is unlikely to be a high quality document. One tip that Matt suggests is to read it aloud to a friend before you post it and ask if it makes sense. So in short make sure that you are writing interesting, compelling content for your site and you should not have much to worry about.