Yours, Etc.: Origins and Uses of 8 Sign-Offs
1825, from Modern Latin genus name, from Latin citrus "citron tree," name of an African tree with aromatic wood and lemon-like fruit, the first citrus fruit to become available in the West. The name, like the tree, is probably of Asiatic origin [OED]. But Klein traces it to Greek kedros "cedar," and writes that the change of dr into tr shows that the word came from Greek into Latin through the medium of the Etruscans. As a noun, "tree of the genus Citrus," from 1885.