This is the 12764th most frequent Russian word.
крестным
"Крестным" means "godfather" in English.
In this sentence, 'крестным' is used as an adjective describing the noun 'отцом' (godfather), indicating the religious role.
Он стал крестным отцом моего сына.
He became the godfather of my son.
Here, 'крестным' is used as a substantive form, referring directly to the role of 'godfather' in religious ceremonies.
Мы пригласили его быть крестным на крестинах.
We invited him to be the godfather at the christening.
In this context, 'крестным' is used metaphorically, emphasizing the act of care associated with being a godparent.