Chord
Middle English cord, from accord. The spelling change in the 18th century was due to confusion with chord2. The original sense was ‘agreement, reconciliation’, later ‘a musical concord or harmonious sound’; the current sense dates from the mid 18th century.
wiktionary
Variant of cord, with spelling alteration due to Latin chorda(“cord”), ultimately from Ancient Greek (Doric) χορδά(khordá), (Ionic) χορδή(khordḗ, “string of gut, the string of a lyre”)
etymonline
chord (n.1)
"related notes in music," 1590s, ultimately a shortening of accord (or borrowed from a similar development in French) and influenced by corde "string of a musical instrument" (c. 1300), which is Latin chorda "catgut, a string" of a musical instrument (see cord (n.)).
English cord as a shortening of accord is attested from mid-14c.; cord meaning "music" is attested in English from late 14c. The spelling with an -h- is first recorded c. 1600, from further confusion with chord (n.2) and perhaps also classical correction. Originally two notes sounded simultaneously; of three or more from 18c.
chord (n.2)
"structure in animals resembling a string," 1540s, alteration of cord (n.), by influence of Greek khorde "gut-string, string of a lyre, tripe," from PIE root *ghere- "gut, entrail."
Meaning "string of a musical instrument" is from 1660s (earlier this was cord). The geometry sense "straight line intersecting a curve" is from 1550s; figurative meaning "feeling, emotion" first attested 1784, from the notion of the heart or mind as a stringed instrument.
