accouplement

from The Century Dictionary.

• noun The act of accoupling or connecting in pairs; union in couples; marriage.
• noun In carpentry: A tie or brace. The entire piece of work formed by a brace and the timbers which it joins.
• noun In architecture, the act of placing two pillars, columns, or pilasters close together, so as to form a pair, in contrast with similar pieces which are spaced more widely. Accouplement is rare in classical buildings as we know them, but is common in modern work.

from the GNU version of the Collaborative International Dictionary of English.

• noun rare The act of coupling, or the state of being coupled; union.
• noun rare That which couples, as a tie or brace.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun rare The act of coupling, or the state of being coupled; union - Caxton
• noun rare That which couples, as a tie or brace