General agreement:
* Harmony
* Agreement
* Accord
* Unity
* Amity
* Consensus
* Entente
* Compatibility
* Congruence
In a musical context:
* Consonance
* Unison
In a legal context:
* Settlement
* Reconciliation
Other synonyms:
* Peace
* Tranquility
* Cooperation
* Understanding
The best synonym will depend on the specific meaning of "concord" in your context.