Children's, Intermediate and Advanced Online English Dictionary & Thesaurus

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barrier island a long narrow island that is parallel to the mainland. A barrier island helps protect the shore from being worn away by the action of the ocean's waves.
barrier reef a ridge of coral running parallel to a coast.
color barrier unspoken social code of racial segregation or discrimination, esp. in sports, education, public service, and the like.
sonic barrier the large increase in aerodynamic resistance experienced by aircraft approaching the speed of sound; sound barrier.
sound barrier a hypothetical barrier to aircraft as they approach the speed of sound, suggested by the abrupt increase in aerodynamic drag near that velocity; sonic barrier.
thermal barrier the maximum flight speed of a given supersonic aircraft in the atmosphere that is set by aerodynamic heating effects.