accordance (n.)

c. 1300, "compliance;" early 14c., "agreement, concurrence, state of being in accord," from Old French acordance "agreeing, reconciliation, harmony," noun of action from acorder "reconcile, agree, be in harmony" (see accord (v.)).

Of things, "conformity, compatibility, harmony," late 14c. The meaning "formal adjustment of a difference, peace treaty" is from late 13c. Phrase in accordance with is attested by 1793 (in Middle English, in accordance of was the usual form).