The title

My interpretation of it is societies view (at the time) that women were delicate, angelic creatures but these women were also "iron jawed" because they were strong enough to stand up and speak for all of womankind for the right to vote.

It's mentioned in the movie (by Mabel Vernon, played by Brooke Smith) that Massachusetts Representative Joseph Walsh gave them that name when he argued that they would not yield to "the nagging of iron-jawed angels."

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