Is sheet a word in the Scrabble Dictionary

Yes, sheet is playable

...and is worth 7 points.

Found in the following dictionaries

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

"Sheet" Definition

noun

A broad rectangular piece of fabric serving as a basic article of bedding.
A broad, flat, continuous surface or expanse: a sheet of ice.
A broad, thin, usually rectangular mass or piece of material, such as paper, metal, glass, or plywood.
A flat or very shallow, usually rectangular pan used for baking.
A large block of stamps printed by a single impression of a plate before the individual stamps have been separated.

adjective

Being in the form of a sheet: sheet aluminum.
Rolled or spread out in a sheet.
Of, relating to, or concerned with the making of sheet metal.

idiom

To Informal Intoxicated; drunk.

verb-transitive

To cover with, wrap in, or provide with a sheet.
To make into sheets.

verb-intransitive

To extend in a certain direction. Used of the sheets of a sail.
To flow or fall in a sheet: rain sheeting against the windshield.