Avogadro's law

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

• noun The principle stating that equal volumes of all gases under identical conditions of pressure and temperature contain the same number of molecules or atoms.

from The Century Dictionary.

• noun See law.

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

• noun the principle that equal volumes of all gases (given the same temperature and pressure) contain equal numbers of molecules