a brother or sister.
Anthropology. a comember of a sib, a unilateral descent group thought to share kinship through a common ancestor.
of or pertaining to a brother or sister: sibling rivalry.

before 1000; late Middle English: relative, Old English; see sib, -ling1

half-sibling, noun Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
sibling (ˈsɪblɪŋ)
1.  a.  a person's brother or sister
 b.  (as modifier): sibling rivalry
2.  any fellow member of a sib
[C19: specialized modern use of Old English sibling relative, from sib; see -ling1]

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

"brother or sister," 1903, modern revival (in anthropology) of O.E. sibling "relative, kinsman," from sibb (adj.) "kinship, relationship" (1500; surviving as sib, chiefly in Scottish), from P.Gmc. *sebjo "blood relation, relative," prop. "one's own" (cf. O.S. sibba, O.Fris., M.Du. sibbe, O.H.G. sippa,
Ger. Sippe, Goth. sibja "kin, kindred"), from PIE s(w)e-bh(o)-, from base *swe- (see idiom). Related to the second element in gossip.
"The word 'sib' or 'sibling' is coming into use in genetics in the English-speaking world, as an equivalent of the convenient German term 'Geschwister' " [E.&C. Paul, "Human Heredity," 1930]
Short form sib is attested from 1957.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

sibling sib·ling (sĭb'lĭng)
One of two or more individuals having one or both parents in common; a brother or sister.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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Encyclopedia Britannica


typically, a brother or a sister. Many societies choose not to differentiate children who have both parents in common from those who share only one parent; all are known simply as siblings. In those societies that do differentiate children on this basis, the former are known as full siblings, and the latter are known as half-siblings. Siblings may be the biological offspring of their parents, or they may be socially classified as such through adoption or the categories used in various descent systems. For instance, in some societies the relationships between certain sets of cousins (most often parallel cousins, the children of one's mother's sister or father's brother) may be the same as those that other forms of reckoning expect between biological siblings. In European and related traditions, the study of child development has included sibling relationships as important factors in personality formation. In many traditional cultures, the rights and obligations that obtain between full siblings are among the most sacrosanct of all the ties that bind kinship groups together.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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Example sentences
The newly hatched sibling seemed to think his older brother was hunky-dory, and they got on famously.
Sibling professors collaborate on a modern-dance program that lets volunteers
  control spotlights to test an economic principle.
The sun's gravitational tug then destabilized the smaller moon's orbit and
  caused it to fall into its larger sibling.
The best treatment for the disease is a bone marrow transplant from an
  immunologically matched sibling.
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