an ancient word for a relative (a sense obsolete by the end of the 15c.), was reintroduced by anthropologists in the first decade of the 20c. with the meaning ‘each of two or more children having one or both parents in common’. It is a kind of popularized technical term, and usefully fills a lexical gap by providing a gender-neutral term for ‘brother or sister’: Small groups drifted through the classroom: mothers and fathers, large numbers of children—Edward’s pupils along with older and younger siblings—P. Lively, 1990. The word is also common in the expression sibling rivalry: Moses…shows more than a hint of sibling rivalry in his attitude to his brother Aaron—C. Raphael, 1972. The word also has a figurative or transferred use, e.g. The line dividing the Kevin Street Sinn Fein organisation and its terrorist sibling, the Provisional IRA, is almost invisible—Daily Tel., 1972.