The act of coupling or joining; a union or pairing of things.
From Old French accouplement, from acoupler + -ment suffix. The -ment suffix creates an abstract noun denoting the action or result of coupling.
In French, 'accouplement' is still the scientific term for mating in animals, but English dropped it in favor of 'coupling' or 'mating'—a good example of how different languages preserve older words.
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