Synonyms:
1. obstruct, forestall, preclude, obviate, thwart. Prevent, hamper, hinder, impede refer to different degrees of stoppage of action or progress. To prevent is to stop something effectually by forestalling action and rendering it impossible: to prevent the sending of a message. To hamper is to clog or entangle or put an embarrassing restraint upon: to hamper preparations for a trip. To hinder is to keep back by delaying or stopping progress or action: to hinder the progress of an expedition. To impede is to make difficult the movement or progress of anything by interfering with its proper functioning: to impede a discussion by demanding repeated explanations.

Antonyms:
1. help, assist.