es·tu·ary /ˈɛsʧəˌwɛri, ˈɛʃ-/
  河口,江口
  Es·tu·a·ry n.; pl. Estuaries   [Written also æstuary.]
  1. A place where water boils up; a spring that wells forth. [Obs.]
  2. A passage, as the mouth of a river or lake, where the tide meets the current; an arm of the sea; a frith.
     it to the sea was often by long and wide estuaries.   --Dana.
  Es·tu·a·ry, a. Belonging to, or formed in, an estuary; as, estuary strata.
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  estuary
       n : the wide part of a river where it nears the sea; fresh and
           salt water mix