Source:
According to Claude Louis Berthollet, "What has long been called fixed, or fixible air, being really an acid in the state of gas, has of late received several new denominations. It has been called aerial acid, as existing very readily in the state of air, or more properly of gas, and plentifully in the atmosphere. The chalky acid, as procurable in large quantities from chalk, or other mild calcareous substances. The name given to it in this essay is derived from the knowledge of its composition, as lately ascertained by the French Chemists to consist of the elementary part of charcoal, named charbone, or char, united with oxygen, or the acidifying principle. Hence it is called, with strict propriety, carbonic acid in general; carbonic acid gas when in the aerial form; and carbonic acid liquor when combined with or dissolved in water."
By French Chemists, Berthollet is generally referring to Lavoisiers oxidation discoveries. The name oxygen is derived from Greek with oxy meaning acid, and gene to mean forming/expression, therefore carbonic acid is simply the union of carbon with oxygen (Laviosiers original degrees of oxidation could not fit the concept of carbon monoxide as it was based on diamond, graphite, coal and carbonic acid)