The term originally came into being to contrast the monarchy form of government where law-making authority vested in a king or queen.
Bouvier’s 1856 American Law Dictionary described republic as follows:
“… government in which there exists an organism by which the opinion of the people … passes over into the public will, that is, law, but in which also the supreme power, or the executive power, returns, either periodically or at stated times, to the people….”
The Constitution of the United States, at Article 4, says:
“The United States shall guarantee to every state in this union a republican form of government, and shall protect each of them against invasion; and on application of the legislature, or of the executive (when the legislature cannot be convened) against domestic violence."