As for definition, I would have to agree with @Fiddle_Playing_Creole_Bastard as there is a sense of refinement, grace, and poise that accompanies this moniker. A beautiful woman can be handsome, but a handsome woman isn’t always beautiful. There is a sense that one can almost see the “breeding” or upper-class insouciance of these women. When seeing such a woman, one might comment that “she appears to be of good stock.” Even with messy, wind-blown hair or wearing limited or no make-up, there is that certain “something” handsome women portray. For me, there is also the sense of “mental toughness” that goes along with “handsome.” It is almost like beauty and mental toughness got together and no amount of crap from the world can disturb her.
As for examples, I would also pick Kate Hepburn and would add Marlene Dietrich. Jackie Onassis dressed casually is a good example (she is beautiful all dressed up and photos exist to prove that, but there is a certain quality of how well she is put together that shows even doing casual activities).
As for little known women who display these characteristics, Dorothy Canfield Fisher is one example. I have to admit that I am struggling mightily to think of a contemporary example other than Martha Stewart and some of the others listed above . . .
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