Is myriad a word in the Scrabble Dictionary

Yes, myriad is playable

...and is worth 12 points.

Found in the following dictionaries

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

"Myriad" Definition

noun

A vast number: the myriads of bees in the hive.
Archaic Ten thousand.
A number .
Ten thousand.

adjective

Composed of numerous diverse elements or facets: the myriad life of the metropolis.
Constituting a very large, indefinite number; innumerable: the myriad fish in the ocean.
Having innumerable aspects or .
Both numerous and .