tributary channel of
This relation can be used for geographic features (e.g. rivers) as well as anatomical structures (veins, arteries)
x tributary_of y if and only if x a channel for the flow of a substance into y, where y is larger than x. If x and y are hydrographic features, then y is the main stem of a river, or a lake or bay, but not the sea or ocean. If x and y are anatomical, then y is a vein.
Deschutes River tributary_of Columbia River
inferior epigastric vein tributary_of external iliac vein