Definition of "unbonnet"

Jacob received them with much gallantry, uncloaking and unbonnetting the ladies, assisted by his two staring and awkward auxiliaries, welcoming their husbands and fathers, and apologizing, as best he might, for the absence of his helpmate;

1827, “A Christmas Party”, in The Atheneum; or, Spirit of the English Magazines, volume VII, second series, Boston: John Cotton, page 73

"Do nothing but rise, unbonnet yourself, and be silent"

1829 May 2, [Walter Scott], Anne of Geierstein; or, The Maiden of the Mist. […], volumes (please specify |volume=I to III), Edinburgh: […] [Ballantyne and Company] for Cadell and Co., […]; London: Simpkin and Marshall, […]

He cast his penetrating glance around, and then unbonnetting to the duke, he said respectfully, […]

1857 (1830), [Mary Shelley], “The Rescue”, in The Fortunes of Perkin Warbeck. A Romance., London: G. Routledge & Co.; New York, page 182

Mrs. Bobaline looked curiously at the shrinking girl, as she unbonneted, and was secretly pleased to see only a meek little face […]

1877, Jeannie H. Grey, Flirtation, Or, Cupid's Shoulder-strap Tactics: A West Point Love Story

Unbonnetting before their betters might be more pleasant than having greatness thrust upon them;

1881, Annie Raine Ellis, chapter XXIII, in Sylvestra, Studies of Manners in England from 1770 to 1800, volume II, London: George Bell and Sons, page 15