Espousal, n.
Etymology: [OF. espousailles, pl., F. épousailles, L. sponsalia, fr. sponsalis belonging to betrothal or espousal. See Espouse, and cf. Sponsal, Spousal.]
1. The act of espousing or betrothing; especially, in the plural, betrothal; plighting of the troths; a contract of marriage; sometimes, the marriage ceremony.
2. The uniting or allying one's self with anything; maintenance; adoption; as, the espousal of a quarrel. The open espousal of his cause. Lord Orford.
Shades of meaning
Fernald has no entry of its own for espousal; he lists it under marriage.
He lists it without comment; the entries above explain its neighbors.