The compound word "发牢骚" is formed through a figurative extension of its literal components: the verb "发" (fā), meaning "to emit" or "to express," is combined with the noun "牢骚" (láosāo), which originally referred to the restless cries or complaints of confined livestock in a pen ("牢"). Over time, "牢骚" semantically shifted to metaphorically denote human grievances, dissatisfaction, or petty complaints. Thus, the entire phrase literally means "to emit complaints," and functions as a verb-object construction meaning "to grumble" or "to vent one's frustrations."