adverb
BAD : My house is near Greenwich Park and thus we'll be able to visit the famous Observatory.
GOOD : My house is near Greenwich Park and so we'll be able to visit the famous Observatory.
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Thus is used only in formal styles: 'All vaccines carry some risk of side effects. Thus emergency equipment and appropriate drugs should be available at all immunization sessions.'
In non-formal styles use so : 'The smell of paint can give you a headache and so it's a good idea to keep the windows open.'