adoptionism
noun
adop·tion·ism ə-ˈdäp-shə-ˌni-zəm 
variants or adoptianism
often capitalized
: the doctrine that Jesus of Nazareth became the Son of God by adoption
adoptionist
ə-ˈdäp-sh(ə-)nist
noun often capitalized 
Word History
Etymology
adoptionism from adoption + -ism, after earlier Adoptionist "member of a sect believing that Jesus is God's son by adoption," altered from earlier Adoptianist, from Medieval Latin Adoptiānus (from Latin adoptiō adoption + -ānus -an entry 1) + -ist entry 1; adoptianism from adoptianist + -ism
First Known Use
1833, in the meaning defined above