barrier

nouns

a structure or object that impedes free movement

barrier

is a type of (narrower)

any structure that makes progress difficult

any condition that makes it difficult to make progress or to achieve an objective

"intolerance is a barrier to understanding"

barrier, roadblock

anything serving to maintain separation by obstructing vision or access

barrier

is a type of (narrower)

a natural object resembling a machine in structure or function

"the mechanism of the ear"; "the mechanism of infection"