The Collaborative International Dictionary of English v.0.48:

matriarch \ma"tri*arch\, n. [L. mater mother + -arch.]
   1. The mother and ruler of a family or of her descendants; a
      ruler by maternal right.
      [1913 Webster]

   2. A woman who dominates or is the most important member of a
      group or organization; in businesses, often the founder or
      owner of the largest interest.
      [PJC]

   3. A venerated old woman.
      [PJC]

WordNet (r) 3.0 (2006):

matriarch
    n 1: a female head of a family or tribe [syn: matriarch,
         materfamilias]
    2: a feisty older woman with a big bosom (as drawn in cartoons)