Anything that has weight and shape has mass. In fact, mass is the quality that gives things weight anywhere there's gravity.

If you think about mass being about weight and shape, you can see how many of its meanings are related. If something is very big we say it has great mass — or is massive. If we talk about a large group of people, we talk about a mass demonstration or a mass of demonstrators. We refer to poor or common people as the masses — there are a lot of them. Doctors refer to tumors inside our bodies as masses.

Definitions of mass

n the property of a body that causes it to have weight in a gravitational field

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the main mass of a thing
the total mass of living matter in a given unit area
critical mass
the minimum mass of fissionable material that can sustain a chain reaction
rest mass
(physics) the mass of a body as measured when the body is at rest relative to an observer, an inherent property of the body
relativistic mass
(physics) the mass of a body in motion relative to the observer: it is equal to the rest mass multiplied by a factor that is greater than 1 and that increases as the magnitude of the velocity increases
the property possessed by a large mass
gravitational mass
(physics) the mass of a body as measured by its gravitational attraction for other bodies
inertial mass
(physics) the mass of a body as determined by the second law of motion from the acceleration of the body when it is subjected to a force that is not due to gravity
atomic mass, atomic weight, relative atomic mass
(chemistry) the mass of an atom of a chemical element expressed in atomic mass units
mass energy
(physics) the mass of a body regarded relativistically as energy
molecular weight, relative molecular mass
(chemistry) the sum of the relative atomic masses of the constituent atoms of a molecule
mass defect, mass deficiency
the amount by which the mass of an atomic nucleus is less than the sum of the masses of its constituent particles
combining weight, eq, equivalent, equivalent weight
the atomic weight of an element that has the same combining capacity as a given weight of another element; the standard is 8 for oxygen
meq, milliequivalent
one-thousandth of an equivalent
Type of:
physical property
any property used to characterize matter and energy and their interactions
fundamental measure, fundamental quantity
one of the four quantities that are the basis of systems of measurement

n a body of matter without definite shape

“a huge ice mass
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coprolith, faecalith, fecalith, stercolith
a hard mass of fecal matter
a large mass of material that is heaped up by the wind or by water currents
a mass that is densely tangled or interwoven
mush, pulp
any soft or soggy mass
a mound of glacial drift
a mass of snow heaped up by the wind
Type of:
an individual 3-dimensional object that has mass and that is distinguishable from other objects

n an ill-structured collection of similar things (objects or people)

an immovable mass of logs blocking a river
a bushy thick mass (especially hair)
Type of:
accumulation, aggregation, assemblage, collection
several things grouped together or considered as a whole

n the common people generally

“separate the warriors from the mass
hoi polloi, masses, multitude, people, the great unwashed
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laity, temporalty
in Christianity, members of a religious community that do not have the priestly responsibilities of ordained clergy
the part of the general public interested in a source of information or entertainment
followers, following
a group of followers or enthusiasts
the audience reached by written communications (books or magazines or newspapers etc.)
TV audience, viewers, viewing audience
the audience reached by television
a group of followers hired to applaud at a performance
any loyal and steadfast following
the fans of a sport or famous person
Type of:
group, grouping
any number of entities (members) considered as a unit

n the property of something that is great in magnitude

“he received a mass of correspondence”
bulk, volume
dollar volume, turnover
the volume measured in dollars
Type of:
the property of relative size or extent (whether large or small)

n (often followed by `of') a large number or amount or extent

batch, deal, flock, good deal, great deal, hatful, heap, lot, mess, mickle, mint, mountain, muckle, passel, peck, pile, plenty, pot, quite a little, raft, sight, slew, spate, stack, tidy sum, wad
deluge, flood, inundation, torrent
an overwhelming number or amount
a mass of hay piled up in a barn for preservation
Type of:
large indefinite amount, large indefinite quantity
an indefinite quantity that is above the average in size or magnitude

adj formed of separate units gathered into a mass or whole

aggregate, aggregated, aggregative
forming a whole or aggregate

v join together into a mass or collect or form a mass

“Crowds were massing outside the palace”
crowd closely
Type of:
crowd, crowd together
to gather together in large numbers

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