Obviate: to make unnecessary; to eliminate the need for something; to do away with; to prevent by effective measures.  

Diet, exercise, sunshine and water obviate the need for most pharmaceutical drugs.  

Obviate comes from the Latin word obviare “to block, to hinder”. The Latin prefix ob means ‘to go against’.  We see this sense in words like obstruct and obstacle.  The rest of the Latin word comes from via, “road, way”.  Obviare is, quite literally, to block the road.  

Some synonyms for obviate are: prevent, circumvent, bypass, avert, counteract, forestall, stave off and hinder.