Pronunciation: (u-nas"tu-mō'sis),[key] —n., —pl.-sesPronunciation: (-sēz).[key] 1. Anat.communication between blood vessels by means of collateral channels, esp. when usual routes are obstructed.
2. Biol.,Geol.connection between parts of any branching system, as veinlets in a leaf or branches of a stream.
3. Surg.,Pathol.a joining of or opening between two organs or spaces that normally are not connected.