Merriam-Webster Collegiate Dictionary - oust

 transitive verb  Etymology: Middle English, from Anglo-French oster, ~er to take off, remove, ~, from Late Latin obstare to ward off, from Latin, to stand in the way, from ob- in the way + stare to stand — more at ob-, stand  Date: 15th century  1.  a. to remove from or dispossess of property or position by legal action, by force, or by the compulsion of necessity  b. to take away (as a right or authority) ; bar, remove  2. to take the place of ; supplant  Synonyms: see eject