Etymology From Old English mersċmealwe, corresponding to marsh + mallow.
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Marsh mallow, a species of mallow, Althaea officinalis, that grows in marshy terrain.
Our common Marsh Mallows have diverse soft, hoary white stalks rising to be three or four foot high, spreading forth many branches.1653, Nicholas Culpeper, The English Physician Enlarged, Folio Society, published 2007, page 180:
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A type of confectionery, originally (since Ancient Egyptian times) made from this plant, but now generally made of sugar or corn syrup, gelatin that has been presoftened in water, gum arabic, flavorings, and sometimes beaten egg whites, all whipped to a spongy consistency.
The Disagreeable Girl is a female of the genus homo persuasion, built around a digestive apparatus that possesses marked marshmallow proclivities.1906, Elbert Hubbard, Love, Life and Work:
It was an apple marshmallow sundae, I recollect. I dug my spoon into it with an assumption of gaiety which I was far from feeling.December 1915, P. G. Wodehouse, “My Battle with Drink”, in Vanity Fair:
Etymology From Old English mersċmealwe, corresponding to marsh + mallow.
1
To soften (literally or figuratively).
For i could still feel her small face in my hands, her lips marshmallowing under the brushing knuckle of my index, the hard press of her capable contoured body.2005, Ken Gunther, Lilith: A Biography:
He didn't know if touching me meant that I would marshmallow up or if he would have to brace himself for a blow.2005, Joylynn Jossel, If I Ruled the World:
1 more example
Various dishes heaped with food were tucked haphazardly all over: mounds of whipped potatoes, medleys of buttered vegetables, marshmallowed sweet potatoes, oyster stuffing, cranberry sauce (fresh from the can) and even more dishes2011, JB Sanders, Glen & Tyler's Honeymoon Adventure: