...so, if you type something where synonyms might be helpful, it should automatically use synonyms...
...but, sometimes you want to type something that looks like it should be autocorrected, but you want it to not autocorrect it...
...and it's not enough that you can do these things - you want them to happen automatically?
I'm sorry, but that is not "a search tool that does what you ask for," that's MAGIC that you want.
If you think a search engine exists that does this better, please tell us all about it, because I think it would be an example of an intelligent machine, in the Turing Test sense.