tedster - 11:14 pm on Dec 14, 2012 (gmt 0)

With regard to synonyms, it's important to recognize that something more complex is going on. Because of phrase-based indexing [webmasterworld.com], an entire phrase can have a "synonym," rather than just an individual word. The same applies to co-occurring vocabulary in general. We're talking about 2, 3, 4 word phrases being treated as a semantic unit in some cases.