1895, from carbon (paper) + copy (n.). A copy on paper made using carbon-paper (paper faced with carbon, used between two sheets for reproduction on the lower of what is drawn or written on the upper). The figurative sense is from 1944. Also as a verb, "send a carbon copy (of something)," and as such often abbreviated c.c.
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Harper, D. (n.d.). Etymology of cc. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/cc