G5206 υἱοθεσία (huiothesía)

KJV renderings: adoption (of children, of sons)
Strong's definition: the placing as a son, i.e. adoption (figuratively, Christian sonship in respect to God)
Derivation: from a presumed compound of G5207 (υἱός) and a derivative of G5087 (τίθημι);

From James Strong's public-domain dictionaries (G), JSON edition by OpenScriptures (CC-BY-SA). Every dotted-underline word in the text links here.