credo n.

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."

Old English creda "article or statement of Christian belief, confession of faith," from Latin credo "I believe" (see credo). Broadening 17c. to mean "a statement of belief on any subject." Meaning "what is believed, accepted doctrine" is from 1610s. Related: Creedal.

A Creed, or Rule of Faith, or Symbol, is a confession of faith for public use, or a form of words setting forth with authority certain articles of belief, which are regarded by the framers as necessary for salvation, or at least for the well-being of the Christian Church. [Philip Schaff, "The Creeds of Christendom," 1877]