- a long, narrow inlet of a river that gradually decreases in depth from mouth to head.
- a long narrow inlet of the seacoast, being a former valley that was submerged by a rise in the level of the sea. Rias are found esp on the coasts of SW Ireland and NW Spain
- Royal Irish Academy
from Spanish ria “estuary, river mouth” (adopted as a geological term first in German, 1886), from Latin ripa “stream bank” (see riparian).