Hinder, impede, obstruct, block, bar, dam all mean to put obstacles in the way of a person or thing or of his or its action.
To hinder is to check or hold back someone or something in action or about to act, move, or start; the term usually stresses harmful or annoying delay or interference with progress.
Sometimes, however, hinder definitely implies prevention.
To impede is to impose upon a person or thing that is moving or in action or in progress something that slows him or it up (as by clogging, hampering, or fettering); the term seldom suggests the stopping of movement or progress, but it commonly implies difficulties so great that movement or action are painfully slow or seriously impaired.
To obstruct is to hinder free or easy passage; the word implies interference with something in motion or in progress or obstacles in the path or channel.
To block (often with up ) is to obstruct so effectively as to close all means of egress or ingress and to prevent all passage.
To bar is to block or to prohibit passage, ingress, or egress. Sometimes the implication of prohibition is so strong that there is no hint of blocking.
To dam (often with up ) is to obstruct with obstacles that prevent a continued flow (as of water, speech, or emotion) and so provide no outlet or exit.