The Collaborative International Dictionary of English v.0.48:

Symbol \Sym"bol\ (s[i^]m"b[o^]l), n. [L. symbolus, symbolum, Gr.
   sy`mbolon a sign by which one knows or infers a thing, from
   symba`llein to throw or put together, to compare; sy`n with +
   ba`llein to throw: cf. F. symbole. Cf. Emblem, Parable.]
   1. A visible sign or representation of an idea; anything
      which suggests an idea or quality, or another thing, as by
      resemblance or by convention; an emblem; a representation;
      a type; a figure; as, the lion is the symbol of courage;
      the lamb is the symbol of meekness or patience.
      [1913 Webster]

            A symbol is a sign included in the idea which it
            represents, e. g., an actual part chosen to
            represent the whole, or a lower form or species used
            as the representative of a higher in the same kind.
                                                  --Coleridge.
      [1913 Webster]

   2. (Math.) Any character used to represent a quantity, an
      operation, a relation, or an abbreviation.
      [1913 Webster]

   Note: In crystallography, the symbol of a plane is the
         numerical expression which defines its position
         relatively to the assumed axes.
         [1913 Webster]

   3. (Theol.) An abstract or compendium of faith or doctrine; a
      creed, or a summary of the articles of religion.
      [1913 Webster]

   4. [Gr. ? contributions.] That which is thrown into a common
      fund; hence, an appointed or accustomed duty. [Obs.]
      [1913 Webster]

            They do their work in the days of peace . . . and
            come to pay their symbol in a war or in a plague.
                                                  --Jer. Taylor.
      [1913 Webster]

   5. Share; allotment. [Obs.]
      [1913 Webster]

            The persons who are to be judged . . . shall all
            appear to receive their symbol.       --Jer. Taylor.
      [1913 Webster]

   6. (Chem.) An abbreviation standing for the name of an
      element and consisting of the initial letter of the Latin
      or New Latin name, or sometimes of the initial letter with
      a following one; as, C for carbon, Na for sodium
      (Natrium), Fe for iron (Ferrum), Sn for tin (Stannum),
      Sb for antimony (Stibium), etc. See the list of names
      and symbols under Element.
      [1913 Webster]

   Note: In pure and organic chemistry there are symbols not
         only for the elements, but also for their grouping in
         formulas, radicals, or residues, as evidenced by their
         composition, reactions, synthesis, etc. See the diagram
         of Benzene nucleus, under Benzene.
         [1913 Webster]

   Syn: Emblem; figure; type. See Emblem.
        [1913 Webster]

WordNet (r) 3.0 (2006):

Sn
    n 1: a silvery malleable metallic element that resists
         corrosion; used in many alloys and to coat other metals to
         prevent corrosion; obtained chiefly from cassiterite where
         it occurs as tin oxide [syn: tin, Sn, atomic number
         50]

V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

SN
       Sequence Number


V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

SN
       Serial Number


V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

SN
       Subscriber Number (MS-ISDN, GSM, mobile-systems)


V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

SN
       Super Node (Kazaa, P2P)


The Free On-line Dictionary of Computing (30 December 2018):

sn

    The country code for Senegal.

   (1999-01-27)