1. formal agreement or harmony between people or groups:

«…との» (意見･利害などの)一致; 調和, 協調 «with» (↔ discord)

e.g. a pact of peace and concord.

a treaty:

(国家間の)友好関係, 平和; (友好)協定, 協約

e.g. a concord was to be drawn up.

2. Grammar agreement between words in gender, number, case, person, or any other grammatical category which affects the forms of the words.

〘文法〙 一致, 呼応〘数･性などで一致した形をとること〙

3. Music a chord that is pleasing or satisfactory in itself.

〘楽〙 協和音(↔ discord)

Middle English: from Old French concorde, from Latin concordia, from concors ‘of one mind’, from con- ‘together’ + cor, cord- ‘heart’.