cardiac adj.

Proto-Indo-European root meaning "heart."

It forms all or part of: accord; cardiac; cardio-; concord; core; cordial; courage; credence; credible; credit; credo; credulous; creed; discord; grant; heart; incroyable; megalocardia; miscreant; myocardium; pericarditis; pericardium; quarry (n.1) "what is hunted;" record; recreant; tachycardia.

It is the hypothetical source of/evidence for its existence is provided by: Greek kardia, Latin cor, Armenian sirt, Old Irish cride, Welsh craidd, Hittite kir, Lithuanian širdis, Russian serdce, Old English heorte, German Herz, Gothic hairto, "heart;" Breton kreiz "middle;" Old Church Slavonic sreda "middle."

mid-13c., herte-brine "lust," later "burning sensation in the esophagus, indigestion" (mid-15c.); see heart (n.) + burn (n.). Compare cardiac for confusion of "heart" and "stomach." A Middle English alternative was herte-brenning "anger, bitterness" (c. 1400), also "heartburn" (mid-15c.).

c. 1400, "of or pertaining to the heart" (a sense now obsolete or rare, replaced by cardiac), from Medieval Latin cordialis "of or for the heart," from Latin cor (genitive cordis) "heart," from PIE root *kerd- "heart." Meaning "heartfelt, proceeding from the heart as the supposed seat of kindly feelings" is from mid-15c. Related: Cordiality.

The noun meaning "something that invigorates" is from late 14c., originally "medicine, food, or drink that stimulates the heart." Meaning "sweet or aromatic liquor" is from 1610s.