He offloaded his old books by donating them to the library.

offloaded 是动词 offload 的过去式。offload 由前缀 off-（表示"离开、去除"）和动词 load（装载）组成，字面意思是"卸下装载"，引申为"摆脱、处理掉不需要的东西"。