The protesters were vociferous in expressing their anger on the streets.

vociferous 是由词根 voc（声音）和后缀 -iferous（产生、携带）组成的形容词，字面意思是"发出声音的"，引申为"大声喧哗的、吵闹的"。在句中形容抗议者表达愤怒时声音很大。