headwater

from WordNet (r) 3.0 (2006)

headwater
    n 1: the source of a river; "the headwaters of the Nile"

from The Collaborative International Dictionary of English v.0.48

Headwater \Head"wa`ter\ (-w[=a]`), n.
   The source and upper part of a stream; -- commonly used in
   the plural; as, the headwaters of the Missouri.
   [Webster 1913 Suppl.]

from Moby Thesaurus II by Grady Ward, 1.0

18 Moby Thesaurus words for "headwater":
      font, fount, fountain, fountainhead, head, headspring, headstream,
      headwaters, mainspring, mine, quarry, riverhead, source, spring,
      springhead, well, wellhead, wellspring

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