Is tartan a word in the Scrabble Dictionary

Yes, tartan 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)

"Tartan" Definition

noun

A plaid fabric.
A small, single-masted Mediterranean ship with a large lateen sail.
A twilled wool fabric or garment having such a pattern.
Any of numerous textile patterns consisting of stripes of varying widths and colors crossed at right angles against a solid background, each forming a distinctive design worn by the members of a Scottish clan.
A garment of tartan design.