Late 16th century: by wrong division of mine uncle.

• uncle from Middle English:

  Both uncle and avuncular (mid 19th century) came through Old French from Latin avunculus ‘uncle on the mother's side’. In the late 16th century people started misinterpreting an uncle as a nuncle, and uncle developed a parallel form nuncle—the opposite of the process seen in adder, apron, and umpire (see pair). In Shakespeare's King Lear the Fool addresses his employer Lear as ‘nuncle’. The expression Uncle Tom Cobley and all comes from an old song called ‘Widdicombe Fair’, dating from around 1800. The song lists the men's names, ending with ‘Uncle Tom Cobley and all’. The independent use of the phrase itself did not develop until around a century later, in the 1930s. Uncle Sam has personified the government or people of the USA since the early 19th century. The name is probably based on the initials US. Since the 1920s Uncle Tom has been an insulting and offensive name for a black man considered to be excessively obedient or servile to whites. The original ‘Uncle Tom’ was an elderly slave who was the central figure of Harriet Beecher Stowe's 1852 anti-slavery novel Uncle Tom's Cabin. See also dutch