Source : Webster's Revised Unabridged Dictionary (1913)

Uncle \Un"cle\, n.
   An eldery man; -- used chiefly as a kindly or familiar
   appellation, esp. (Southern U. S.) for a worthy old negro;
   as, ``Uncle Remus.'' [Colloq.]

         Plain old uncle as he [Socrates] was, with his great
         ears, -- an immense talker.              --Emerson.

Uncle \Un"cle\, n. [OE. uncle, OF. oncle, uncle, F. oncle, fr.
   L. avunculus a maternal uncle, dim. of avus a grandfather;
   akin to Lith. avynas uncle, Goth. aw? grandmother, Icel.
   [=a]i great grandfather.]
   1. The brother of one's father or mother; also applied to an
      aunt's husband; -- the correlative of aunt in sex, and of
      nephew and niece in relationship.

   2. A pawnbroker. [Slang] --Thackeray.

   {My uncle}, a pawnbroker. [Slang]

   {Uncle Sam}, a humorous appellation given to the United
      States Government. See {Uncle Sam}, in Dictionary of Noted
      Names in Fiction.

Source : WordNet®

uncle
     n 1: the brother of your father or mother; the husband of your
          aunt [ant: {aunt}]
     2: a source of help and advice and encouragement; "he played
        uncle to lonely students"