Real Dictionary

Avogadro's law in American English
the principle, formulated by Avogadro, that equal volumes of all gases under identical conditions of temperature and pressure contain equal numbers of molecules
noun: the principle that equal volumes of all gases at the same temperature and pressure contain the same number of molecules. Thus, the molar volume of all ideal gases at 0° C and a pressure of 1 atm. is 22.4 liters

Avogadro's law in British English
noun: the principle that equal volumes of all gases contain the same number of molecules at the same temperature and pressure