Is zapper a word in the Scrabble Dictionary

Yes, zapper is playable

...and is worth 21 points.

Found in the following dictionaries

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

"Zapper" Definition

noun

Slang A destructive device, especially one that destroys by means of electric current or radiation: a bug zapper.
Slang A remote-control device for switching a television set on and off and for changing channels.