Not sure of op's reason, but a lot of people believe that using LSI keywords helps a site rank. Instead of using the same keyword over and over, you say the same thing, but with different LSI keywords. The theory is that G likes LSI keywords.

LSI stands for Latent Semantic Indexing and it means words like the your keywords but words that help put the keyword in some sort of context. For example the keyword ‘footbal boots’ could be surrounded by references to the Adidas Predator which helps give more meaning to the main keyword you’re optimising for.

If you want to find a list of LSI keywords use the Google Keyword tool and see what comes up around your chosen keyword.

LSI stands for Latent Semantic Indexing and is one specific algorithm that the search engines use to evaluate site content through related keywords.

LSI keywords are related words that occur naturally when you are discussing a topic. For example, if you are talking about feeding dogs, then dog food, bowls, wet, dry -- are some terms that might show up.

LSI also takes the distance of the prime keyword to the related keywords into account.

I expect LSI keywords to become more important. Google has said that they are looking for more than just the explicit keywords - to me, when you express that mathematically, that means LSI. Google is looking for natural patterns and word choices that occur in well written articles.

I recommend the site Latent Semantic Indexing. It gives you the LSI terms from the sites which are currently topping the Google rankings for a given keyword. I like it better than the Google keyword tool, although that is helpful as well.