Sentence:  It was an apple <WSD>marshmallow</WSD> sundae, I recollect. I dug my spoon into it with an assumption of gaiety which I was far from feeling. 
Meaning of the word marked with <WSD> tags:  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 pre-softened in water, gum arabic, flavorings, and sometimes beaten egg whites, all whipped to a spongy consistency. (from 19th c.)