siblinghoodn.
/ˈsɪblɪŋhʊd/, U.S. /ˈsɪblɪŋˌ(h)ʊd/ The state, condition, or fact of being a sibling; sisterhood or brotherhood.
ΘΚΠ
society > society and the community > kinship or relationship > kinsman or relation > sibling > [noun] > siblinghood
siblingship1941
siblinghood1947
1947 Advancem. Sci. Sept. 219/1 The ties latent in parentage and siblinghood are prevented from formalised expression in the social organisation.
1982 R. Sheppard & M. Valpy National Deal v. 103 There are all the connections of close siblinghood: a familiarity that is at once affectionate and nasty.
2015 E. McCracken in A. Flourney Turner House (back cover) This book is..about aging and parenthood and above all that misunderstood lifelong union, siblinghood.
This is a new entry (OED Third Edition, June 2022).
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n.1947