sibling

Origin

First use appears c. 1903, a modern revival of Old English sibling (“relative, a relation, kinsman”), equivalent to sib + -ling. Compare Middle English siblynges pl, sib, sibbe (“relative; kinsman”), German Sippe. The term apparently meant merely kin or relative until the 20th century when it was applied in a way that aided the study of genetics, which led to its specialized use. For example, the OED has a citation in 1902 in which sibling must be defined for those who do not know the intended meaning.