S

1. The symbol for the element sulfur.
2. The symbol for entropy (sense 1).

The symbol for the element sulfur.

The noun has 4 meanings:

Meaning #1: an abundant tasteless odorless multivalent nonmetallic element; best known in yellow crystals; occurs in many sulphide and sulphate minerals and even in native form (especially in volcanic regions)
  Synonyms: sulfur, sulphur, atomic number 16

Meaning #2: the cardinal compass point that is at 180 degrees
  Synonyms: south, due south

Meaning #3: a unit of conductance equal to the reciprocal of an ohm
  Synonyms: mho, siemens, reciprocal ohm

Meaning #4: the 19th letter of the Roman alphabet