S: (n) obstacle, obstruction (something immaterial that stands in the way and must be circumvented or surmounted) "lack of imagination is an obstacle to one's advancement"; "the poverty of a district is an obstacle to good education"; "the filibuster was a major obstruction to the success of their plan"
S: (n) barrier, roadblock (any condition that makes it difficult to make progress or to achieve an objective) "intolerance is a barrier to understanding"