Longman Dictionary of Contemporary English - mass

mass ~1 n 1 »LARGE AMOUNT« a) a large amount of a substance, liquid, or gas, that does not have a clear shape  (The food had all congealed into a sticky mass.) + of  (A mass of almost pure white cloud lay below us.) b) a mass of a large amount or quantity of something  (a huge mass of data | The yard was just a mass of weeds.) c) masses of BrE informal a large amount of something, or a lot of people or things  (Masses of books covered every surface in the room. | We still had masses of time to spare.) 2 »CROWD« a large crowd + of  (There was a mass of people around the club entrance.) a solid mass  (The road was blocked by a solid mass of protesters.) 3 the masses all the ordinary people in society who do not have power or influence, and are thought of as not being very educated 4 the mass of people/workers/the population etc most of the people in a group or society; the majority  (The mass of black children there have fewer educational opportunities than their white counterparts.) 5 »SCIENCE« technical in science, mass is the amount of material in something  (the mass of a star) ~2 adj only before noun 1 involving or intended for a very large number of people  (Radio can reach mass audiences. | a mass protest) 2 mass murderer someone who has murdered a lot of people ~3 v to come together, or make people or things come together, in a large group  (grey clouds massing behind the mountains | The country massed several divisions of troops along its border.)