Sibling is an Old English word meaning 'relative' that died out in Middle English and was deliberately revived in 1903 by anthropologists who needed a gender-neutral term for brother or sister.
A brother or sister; one of two or more children sharing a parent.
From Old English sibling, meaning 'a relative, kinsman,' from sibb (kinship, peace, relationship) plus the suffix -ling. The word fell out of use in Middle English and was revived by anthropologists in 1903 as a gender-neutral term for 'brother or sister.' Its modern meaning is narrower than the original, which encompassed any blood relative. Key roots: sibb (Old English: "kinship, peace, relationship").