confluence

Short definition from Wiktionary

Noun

1. 1
   The act of combining that occurs where two rivers meet.
2. 2
   The act of combining that occurs where two rivers meet: The place where two rivers, streams, or other continuously flowing bodies of water meet and become one, especially where a tributary joins a river.
3. 3
   The act of combining that occurs where two rivers meet: The stream or body formed by the junction of two or more streams; a combined flood.
4. 4
   A convergence or combination of forces, people, or things.
5. 5
   The proportion of cells, in a culture medium, that adhere to each other.
6. 6
   A property describing which terms can be rewritten with other, equivalent terms.

Verb

1. 1
   To join together into one stream.