Is thirst a word in the Scrabble Dictionary

Yes, thirst 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)

"Thirst" Definition

noun

A sensation of dryness in the mouth and throat related to a need or desire to drink.
An insistent desire; a craving: a thirst for knowledge.
The desire to drink.
A sensation of dryness in the mouth and throat associated with a desire for liquids.
The bodily condition (as of dehydration) that induces this sensation.

verb-intransitive

To feel a need to drink.
To have a strong craving; yearn.

verb

To feel suffer thirst.
To crave vehemently and urgently.