a number of things of the same kind, growing or held together; a bunch: a cluster of grapes.
a group of things or persons close together: There was a cluster of tourists at the gate.
U.S. Army. a small metal design placed on a ribbon representing an awarded medal to indicate that the same medal has been awarded again: oak-leaf cluster.
Phonetics. a succession of two or more contiguous consonants in an utterance, as the str- cluster of strap.
Astronomy. a group of neighboring stars, held together by mutual gravitation, that have essentially the same age and composition and thus supposedly a common origin. Compare globular cluster, open cluster, stellar association.
verb (used with object)
to gather into a cluster or clusters.
to furnish or cover with clusters.
verb (used without object)
to form a cluster or clusters: The people clustered around to watch.

before 900; Middle English; Old English cluster, clyster bunch; cognate with Low German kluster

clusteringly, adverb
clustery, adjective
intercluster, adjective
subcluster, noun
unclustered, adjective
unclustering, adjective

8. group, gather, throng, crowd, bunch. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
cluster (ˈklʌstə)
1.  a number of things growing, fastened, or occurring close together
2.  a number of persons or things grouped together
3.  (US) military a metal insignia worn on a medal ribbon to indicate a second award or a higher class of a decoration or order
4.  military
 a.  a group of bombs dropped in one stick, esp fragmentation and incendiary bombs
 b.  the basic unit of mines used in laying a minefield
5.  astronomy an aggregation of stars or galaxies moving together through space
6.  a group of two or more consecutive vowels or consonants
7.  statistics a naturally occurring subgroup of a population used in stratified sampling
8.  chem
 a.  a chemical compound or molecule containing groups of metal atoms joined by metal-to-metal bonds
 b.  the group of linked metal atoms present
9.  to gather or be gathered in clusters
[Old English clyster; related to Low German Kluster; see clod, clot]

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
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Word Origin & History

O.E. clyster "cluster," probably from the same root as clot. The verb is from late 14c. Clusterfuck "bungled or confused undertaking" is from 1969, U.S. military slang, earlier "orgy" (1966).
Online Etymology Dictionary, © 2010 Douglas Harper
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Computing Dictionary

cluster definition

1. Multiple servers providing the same service. The term may imply resilience to failure and/or some kind of load balancing between the servers. Compare RAIS.
2. An elementary unit of allocation of a disk made up of one or more physical blocks.
A file is made up of a whole number of possibly non-contiguous clusters. The cluster size is a tradeoff between space efficiency (the bigger is the cluster, the bigger is on the average the wasted space at the end of each file) and the length of the FAT.

The Free On-line Dictionary of Computing, © Denis Howe 2010
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Encyclopedia Britannica


Atoms and molecules are the smallest forms of matter typically encountered under normal conditions and are in that sense the basic building blocks of the material world. There are phenomena, such as lightning and electric discharges of other kinds, that allow free electrons to be observed, but these are exceptional occurrences. It is of course in its gaseous state that matter is encountered at its atomic or molecular level; in gases each molecule is an independent entity, only occasionally and briefly colliding with another molecule or with a confining wall.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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Example sentences
Among these flies are cluster flies, so called because of their habit of
But what is emerging from this research is a cluster of biological markers that
  plant the bad seed in the brain.
Bees live on stored honey and pollen all winter, and cluster into a ball to
  conserve warmth.
The rose produces up to a dozen flowers per cluster.
Image for cluster
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