Open English Wordnet
Nouns
(n)obstruction, obstructor, obstructer, impediment, impedimentaany structure that makes progress difficult
(n)obstacle, obstructionsomething 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”