Definitions for siblingˈsɪb lɪŋ
Random House Webster's College Dictionary
a brother or sister.
Anthrop. a member of a sib.
Origin of sibling:
bef. 1000; late ME: relative, OE; see sib , -ling1
a person's brother or sister
Kernerman English Learner's Dictionary
a sister or brother
How many siblings do you have?
A person who shares same parents. One's brother or sister.
Origin: 1903, modern revival of sibling, equivalent to . Compare sib. The term apparently meant merely kin or relative until the 20th century when its necessity for the study of genetics led to its broader use. For example, the OED has a 1903 citation in which "sibling" must be defined for those who don't know the intended meaning.