Final answer:
The word 'abruptly' means suddenly and unexpectedly, describing how quickly something happens without warning.
Step-by-step explanation:
The word abruptly in the provided sentence means suddenly and unexpectedly. It is an adverb that modifies the verb thinned, indicating how quickly and without warning the change in the stream of movement occurred. To illustrate, in the sentence, "Pierre quickly ran through the main points of his argument," the adverb quickly serves a similar function to 'abruptly' by describing how Pierre ran through his points. As another example, in "She threw down the gauntlet quite suddenly," the adverb suddenly is enhanced by the qualifier quite, showing that the action of throwing was done unexpectedly, much like how the stream movement changed in the original sentence.
The word ABRUPTLY means suddenly and unexpectedly. It describes an action or event that occurs without warning or preparation. For example, if a stream of movement abruptly thinned, it means that the movement suddenly and unexpectedly reduced in numbers or intensity.