1903, modern revival of Old English sibling (“relative, a relation, kinsman”), equivalent to sib + -ling. Compare Middle English sib, sibbe (“relative; kinsman”). The term apparently meant merely kin or relative until the 20th century when its necessity for the study of genetics led to its specialized use. For example, the OED has a 1903 citation in which "sibling" must be defined for those who don't know the intended meaning.
- "1903 K. PEARSON in Biometrika II. 369 These [calculations] will enable us..to predict the probable character in any individual from a knowledge of one or more parents or brethren (‘siblings’, = brothers or sisters)." ("Sibling," OED.)
sibling (plural siblings)