correspondence (n.)

early 15c., "congruence, resemblance, harmony, agreement," from Medieval Latin correspondentia, from correspondentem (nominative correspondens), present participle of correspondere "correspond, harmonize, reciprocate," from assimilated form of com "together, with (each other)" (see com-) + respondere "to answer" (see respond). Sense of "communication by letters" is first attested 1640s; that of "the letters which pass between correspondents" is from 1771.