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Webster 1913 Edition

Noun.

[

Ana

stomosing +

branch

A branch of a river that reënters, or anastomoses with, the main stream; also, less properly, a branch which loses itself in sandy soil.

[Australia]

anabranch ‎(plural anabranches)

(hydrology, of a water channel) A diverging branch of a river, creek, or stream which re-enters the main stream.
- Col. Jackson
  Such branches of a river as after separation reunite, I would term anastomosing branches; or, if a word might be coined, anabranches, and the islands they form branch islands.

National Weather Service (accessed 2010-03-23), “Anabranch”, in Glossary, National Oceanic and Atmospheric Administration