The derivation
Both de Vaan and Ernout-Meillet trace cor, cordis to one of the most secure and widely attested roots in the entire Indo-European family: PIE nominative *ḱērd, genitive *ḱr̥d-o/es "heart," continuing in Proto-Italic as *kord-, *kordo/es- (de Vaan, EDL s.v. cor; Ernout-Meillet, DELL s.v. cor). De Vaan lays out the cognate row at length: Old Irish cride "heart," Welsh craidd; Hittite ker / kard(i)- "heart, center," Palaic kart-, Cuneiform Luwian zart-, Hieroglyphic Luwian zart(i)-; Sanskrit hŕ̥d-, nominative hārdi; Greek καρδία (Attic), κραδίη (Homeric) — the very word treated in the kardia and ētor crown essays; Armenian sirt; Lithuanian širdìs; Gothic hairtō, Old High German herza, Old Norse hjarta; Tocharian A hi "will," Tocharian B karyan "hearts." De Vaan notes the Latin paradigm was rebuilt on the oblique-case stem *ḱr̥d-, and that the diminutive corculum preserves the older athematic stem directly (de Vaan, EDL s.v. cor).
Ernout-Meillet add the semantic history that de Vaan's root-focused entry only implies. In ordinary Latin cor names, first, the physical organ; but from the earliest attested usage it doubles as "cœur en tant que siège de l'âme" — the heart as seat of the soul — and Cicero states the philosophical stakes outright: "aliis cor ipsum animus uidetur," to some the heart itself seems to be the animus (Cic., Tusc. 1.18); elsewhere he sets cor against the brain and against Empedocles's blood as rival seats of thought (Tusc. 1.41, discussed also under mens). Isidore later states flatly that "in corde omnis sollicitudo et scientiae causa manet" — in the heart resides all anxiety and the source of knowledge (Isid., Orig. 11.1.118) — and a scholiast on Persius adds that physici held "homines corde sapere," that people think with the heart (Schol. Persius 1.12, both cited DELL). Ernout-Meillet trace the derivational family straight through this doubled sense: compounds built on intelligence and sensibility both — excors "senseless," sōcors "inert, lacking energy," tied "plutôt à la notion d'intelligence," more to the notion of intelligence; concors, discors and their kin, tied "à la notion de sensibilité," to the notion of feeling — plus misericors, "tender-hearted," a favorite Ciceronian coinage of the late Republic (Ernout-Meillet, DELL s.v. cor).
Root
- PIE *ḱērd, gen. *ḱr̥d-o/es "heart" — de Vaan and Ernout-Meillet agree exactly. This is among the best-attested roots in Indo-European: Hittite kard(i)-, Sanskrit hŕ̥d-, Greek καρδία / κραδίη, Armenian sirt, Lithuanian širdìs, Gothic hairtō, Old Irish cride, Tocharian B karyan.
- The Latin diminutive corculum < *kord-kelo- preserves the athematic oblique stem as its derivational base (de Vaan, EDL s.v. cor) — a small grammatical fossil of the older paradigm.
In the corpus
869 occurrences across 136 works — the rarest of the six Latin words gathered here, and spread thin rather than concentrated. Silius Italicus's Punica leads at 62 occurrences; Pliny's Naturalis Historia follows with 59; a collection of Augustine's letters with 50; Tertullian's Adversus Marcionem with 45; Statius's Thebais with 39. Vergil's Aeneid contributes 28, including the philosophically loaded line from Lucretius (De Rerum Natura 4.53, corde) that Ernout-Meillet cite in the same breath as Cicero's heart-versus-brain question. Where mens is the everywhere-word of Roman prose and animus dominates history and rhetoric by the thousands, cor stays comparatively rare — a word reached for at the moments a writer wants the older, more physical, more contested seat of thought and feeling, not the settled philosophical vocabulary mens had become.
The word's world
Cor is the one Latin soul-word whose etymology is beyond real dispute — the same PIE root that gives Greek its καρδία and κραδίη, English its own "heart," and half the Indo-European family a nearly identical word — and yet its Roman career is a story of contested territory. Cicero records the debate without settling it: is the animus the heart itself, or does thought sit instead in the brain, or, as Empedocles proposed, in the blood? Isidore centuries later still calls the heart the seat of "all anxiety and the source of knowledge," and a scholiast on Persius states as settled physiology what Cicero had only entertained as one option among several: that people think with the heart. The derivational family shows the same double life the Greek kardia essay documents for its own word: some compounds (excors, sōcors) point to intelligence, others (concors, discors, misericors) to feeling — the same ambiguity between thinking-organ and feeling-organ that runs through nearly every ancient culture's word for the heart, Hebrew's lēb very much included.
Authorities: de Vaan, Etymological Dictionary of Latin and the other Italic Languages (Brill 2008) s.v. cor (p. 135; opened directly from the audited library, the audited library). Ernout & Meillet, Dictionnaire étymologique de la langue latine (4th ed., Klincksieck) s.v. cor (opened directly, the audited library). Lewis & Short entry and corpus figures from the live Logoi corpus record — receipt soul-word-journey-v0. Cross-references: kardia, ētor, mens, animus, lēb.