matriarch

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A woman who rules a family, clan, or tribe.
• noun A woman who dominates a group or an activity.
• noun A highly respected woman who is a mother.

from The Century Dictionary.

• noun The wife of a patriarch.
• noun A woman who holds (to some extent or in some respect) in a family or tribe a position analogous to that of a patriarch. See matriarchy.

from the GNU version of the Collaborative International Dictionary of English.

• noun The mother and ruler of a family or of her descendants; a ruler by maternal right.
• noun 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.
• noun A venerated old woman.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A female leader of a family, a tribe or an ethnic or religious group.
• noun A female founder of a political or religious movement, an organization or an enterprise.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a feisty older woman with a big bosom (as drawn in cartoons)
• noun a female head of a family or tribe