I've been looking at the topic of Latent Semantic Indexing (LSI) which is what major search engines use to identify which keywords are related to each other; examples are, if you put into google 'Cleethorpes' you will also get pages about Grimsby and Lincolnshire. I've now found that there is a special character you can use in google searches which can show you what keywords are related. This is the Tilde operator.

In mathematics, the tilde means 'is roughly equal to', and is sometimes written as a squiggly equals sign (≈). The Tilde character is similar, but just one squggly line (~) and this appears on a uk keyboard above the hash character (not sure where it is on a US keyboard, since I don't have one).

Using the Tilde character in search is very useful for determining related keywords. Related keywords are used in SEO techniques such as Long Tail Keywords, SEO zooming, and Keyword Association Manipulation, so having a tool that can let you peer into some of the darker inner workings of Google's LSI processes means you have more information available with which to inform your SEO strategies.