Is leash a word in the Scrabble Dictionary

Yes, leash is playable

...and is worth 8 points.

Found in the following dictionaries

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

"Leash" Definition

noun

A chain, rope, or strap attached to the collar or harness of an animal, especially a dog, and used to lead it or hold it in check.
A set of three animals, such as hounds.
A set of three.
Control or restraint: emotions kept in leash.
A line for leading or restraining an animal.

verb-transitive

To restrain with or as if with a leash.