heartstring is a compound of heart and string, originally referring to the tendons or nerves once believed to brace the heart; both elements of Old English origin (heorte, streng). Morphologically, the word is best read through the components named in the history, with the modern spelling preserving a compound structure rather than a single unanalyzable stem. In present English, the noun sense is "one's deepest feelings or affections (usually plural)", so the historical development ends in a clearly identifiable modern dictionary use. The same base also appears in related forms such as heart and string. Its semantic neighborhood includes affection, emotion, and feeling, which helps locate the modern sense without adding a separate etymological claim. The named historical forms include Old English heorte and Old English streng.