suction cup

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

• noun A cup-shaped device, usually of plastic or rubber, designed to adhere to a flat surface by means of suction.

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

• noun A device comprised of a flexible material formed into a three-dimensional shape with one flat open face which, when pressed against a flat surface will adhere to that surface due to the lower pressure in between the flexible material and the flat surface as compared to the pressure outside the flexible material.

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

• noun a cup-shaped device (made of rubber, glass, or plastic) that produces a partial vacuum; used to adhere or draw something to a surface