c. 1300, "branched or divided in two parts," past-participle adjective from fork (v.). Of roads from 1520s; from 1550s as "pointing more than one way." In 16c.-17c. sometimes with a suggestion of "cuckold," on the notion of "horned." Forked tongue as a figure of duplicitous speech is from 1885, American English. Double tongue in the same sense is from 15c.
"cunning, deceitful, habitually duplicitous, unscrupulous, destitute of political morality," 1570s, from Niccolo Machiavelli (1469-1527), Florentine statesman and author of "Il Principe," a work advising rulers to place advantage above morality. A word of abuse in English well before his works were translated ("The Discourses" in 1636, "The Prince" in 1640), in part because his books were Indexed by the Church, in part because of French attacks on him (such as Gentillet's, translated into English 1602). Related: Machiavellianism.
