A natural body of running water flowing on or under the earth WordNet 3.0 & Open English WordNet

A watercourse is the channel that a flowing body of water follows. Wikipedia

A stream is a continuous body of surface water flowing within the bed and banks of a channel. Wikipedia

The channel that a flowing body of water follows Wikipedia Disambiguation

Body of moving water. Wikipedia Disambiguation

Any flowing body of water Wikidata

Body of water with current within bed and stream banks Wikidata

Small stream Wikidata

part of river basin formed by lakes connected with short rivers, straits or narrows.; system of surface and ground waters flowing into a common terminus such as the sea, lake or aquifer Wikidata

A small river or large creek; a body of moving water confined by banks. OmegaWiki

A natural stream arising in a given drainage basin but not wholly dependent for its flow on surface drainage in its immediate area, flowing in a channel with a well-defined bed between visible banks or through a definite depression in the land, having a definite and permanent or periodic supply of water, and usually, but not necessarily, having a perceptible current in a particular direction and discharging at a fixed point into another body of water. OmegaWiki

A small river; a large creek; a body of moving water confined by banks. Wiktionary

Small river. Wiktionary (translation)