ObstacleAn obstacle is something that keeps you from making progress or taking some action. It can be a physical object or an attitude.
Ex: The only obstacle to my success at work was the lack of time to finish decorating the display window for Christmas. I vowed to stay up all night if necessary.
Ex: The massive oak tree in the back garden proved too large an obstacle to my parents' ability to grow a large variety of vegetables. Rather than remove the ancient tree, they planted a garden in the front yard.
An obstacle course is a course designed with a variety of structures to make it difficult for a competitor to complete it. A temporary obstacle to progress is called a snag.
Ex: A foot race that is similar to an obstacle course is the steeplechase which involves jumping over streams and hurdling walls over a predetermined distance.
Ex: The remodel of my kitchen hit a snag when the contractor discover unsafe wiring. Before he could continue, he had to get an electrician to rewire the entire house.
ObstructTo obstruct is to make it difficult to pass, sometimes by using an obstacle. It can also mean to block something from sight.
Ex: Many deer hunters use a platform built in a tree as a perch instead of hunting while walking because it prevents low branches and bushes from obstructing their view of the animals.
Ex: Last night's storm blew down a large tree across the street, and it obstructed our passage to the motorway. We had to find an alternative route to work.
An obstruction is something that closes up a passage with an obstacle. In medicine, an obstruction is a structure that prevents the flow of bodily fluids. Someone who prevents progress is an obstructionist.
Ex: John had emergency surgery on Sunday to eliminate a bowel obstruction. Not only was it very painful, the obstruction could have endangered his life.
Ex: Claude enjoyed his role as an obstructionist so much that he voted against every proposal that the student council considered to improve the school lunches. As a result, no changes were made.