Marriage or adoption (8)
I believe the answer is:
espousal
This clue is a double definition.
'marriage' is the first definition.
(espousal is a kind of marriage)
'adoption' is the second definition.
(thesaurus)
'or' acts as a link.
(Other definitions for espousal that I've seen before include "old-fashioned marriage" , "Adoption, support (of)" , "Adoption (of a cause) - USA's pole (anag)" , "Action of adopting (a cause)" , "Acceptance with approval" .)