Is slump a word in the Scrabble Dictionary

Yes, slump is playable

...and is worth 13 points.

Found in the following dictionaries

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

"Slump" Definition

noun

A drooping or slouching posture: read defeat in the slump of his shoulders.
A sudden falling off or decline, as in activity, prices, or business: a stock market slump; a slump in farm prices.
An extended period of poor performance, especially in a sport or competitive activity: a slump in a batting average.
See grunt.
The act or an instance of slumping.

verb-intransitive

To decline suddenly; fall off: Business slumped after the holidays.
To droop, as in sitting or standing; slouch.
To fall or sink heavily; collapse: She slumped, exhausted, onto the sofa.
To perform poorly or inadequately: The team has been slumping for a month.
To sink or settle, as into mud or slush.

verb

To fall or sink suddenly.
To drop or slide down suddenly .
To assume a drooping posture or carriage .
To go into a slump .