expression, godan verb (-su)
exchange promises; make a mutual pledge
Rare, somewhat formal expression for exchanging vows or promises, often in a solemn or literary context. More common alternatives include 約束を交わす or 誓いを交わす.
二人は固い約を交わした。
The two exchanged firm promises.
Composed of 約 (promise, vow) and 交わす (to exchange). The exact historical derivation is uncertain, but the phrase follows a common pattern for mutual actions.