[1] : The Collaborative International Dictionary of English v.0.48

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.
   =ai 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.
      1913 webster

   2. a pawnbroker. slang --thackeray.
      1913 webster

   3. 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.
      webster 1913 suppl.

   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.
      1913 webster
see also:
my uncle uncle sam 

[2] : WordNet (r) 2.0

uncle sam
     n : a personification of the united states government

[3] : U.S. Gazetteer (1990)

uncle sam, la
  zip codes: 70792

Sam >> S Words
Sam, definition of term: Sam
sam_pag1.html

Dutch Uncle >> D Words
Dutch Uncle, definition of term: Dutch Uncle
dutch+uncle_pag1.html