anastomosis

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The connection of separate parts of a branching system to form a network, as of leaf veins, blood vessels, or a river and its branches.
• noun Medicine The surgical connection of separate or severed tubular hollow organs to form a continuous channel, as between two parts of the intestine.

from The Century Dictionary.

• noun In surgery, the establishment of communication between two canals or two portions of the same canal, usually the digestive tract, not previously in continuity.
• noun In zoology and anatomy, the union, intercommunication, or inosculation of vessels of any system with one another, or with vessels of another system, as the arteries, veins, and lymphatics. In surgery, after ligation of an artery, collateral circulation is established by arterial anastomosis.
• noun The interlacing or network of any branched system, as the veins of leaves or the nervures of insects' wings. See cut under venation.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Anat. & Bot.) The inosculation of vessels, or intercommunication between two or more vessels or nerves, as the cross communication between arteries or veins.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun a cross-connection between two blood vessels
• noun an interconnection between any two channels, passages or vessels
• noun medicine the surgical creation of a connecting passage between blood vessels or other channels

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a natural or surgical joining of parts or branches of tubular structures so as to make or become continuous