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)

Moby Thesaurus II by Grady Ward, 1.0:

66 Moby Thesaurus words for "matriarch":
   Methuselah, abbess, antediluvian, antique, back number, chatelaine,
   conservative, dad, dam, dame, dodo, dowager, elder, first lady,
   fogy, fossil, foster mother, fud, fuddy-duddy, genetrix, goodwife,
   governess, grande dame, granny, great lady, has-been, homemaker,
   housewife, longhair, ma, madam, mam, mama, mammy, mater,
   materfamilias, maternal ancestor, matron, mid-Victorian, mistress,
   mom, mommy, mossback, mother, mother superior, mummy, old believer,
   old crock, old dodo, old fogy, old liner, old man, old poop,
   old woman, old-timer, patriarch, pop, pops, reactionary,
   regular old fogy, relic, square, starets, stepmother,
   the old woman, traditionalist