1. A loud, domineering woman.
2. A woman of great stature, strength, and courage.
Etymology: 14th century, from Latin virago, from vir, "man". Think "virile".
Definition #1 has a synonym: termagant, defined as "an overbearing, nagging woman; a shrew".
Definition #2 appears to have come first, with origins in ancient Greece and Rome, and refers to a woman who has heroically exceeded what was thought possible for her gender. More details at the the ever-handy Wikipedia.
This word (as definition #1) appeared in the most recent Doctor Who episode ("The Crimson Horror").
