Is river a word in the Scrabble Dictionary

Yes, river is playable

...and is worth 9 points.

Found in the following dictionaries

Enable (Words with friends)
SOWPODS (Collins Scrabble Words)
OTCWL2014 (NASPA Word List 2014)
TWL06 (NASPA List 2006)

"River" Definition

noun

A large natural stream of water emptying into an ocean, lake, or other body of water and usually fed along its course by converging tributaries.
A stream or abundant flow: a river of tears.
A natural stream of water of usually considerable volume.
Something resembling a river .
Large or overwhelming quantities .

idiom

Up the river Slang In or into prison.