tongue depressor

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A thin blade for pressing down the tongue during a medical examination of the mouth and throat.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A long, narrow, smooth piece of wood designed to depress the tongue, to allow for examination of the rear of the oral cavity.
• noun less commonly Any device used to depress the tongue.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a thin depressor used to press the tongue down during an examination of the mouth and throat