He gave vent to the frustration that had been building up inside him.

gave 是动词 give 的过去式，意思是"给予"。 vent 是名词，本义是"通风口、排气孔"，引申为"发泄的途径"。 to 在这里是介词，表示方向或对象。 gave vent to 是一个固定短语，字面意思是"给...一个发泄的出口"，实际含义是"发泄(情绪)"。