The act or ceremony of marrying; espousal; a betrothal or the adoption of a cause.
From espouse plus the -ment suffix, which creates abstract nouns indicating an action or state. This variant existed in Middle English but is now archaic, replaced by espousal.
Espousement is basically a fancy way of saying 'the marrying process,' but it almost sounds musical—you can imagine it as a poetic term a Renaissance poet might use for a wedding ceremony!
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