Compound of 積(つ)み (tsumi, the 連(れん)用(よう)形(けい) (ren'yōkei, “stem or continuative form”) of the verb 積(つ)む (tsumu, “to load; to stack”)) + 荷(に) (ni, “load; burden”).
積(つ)み荷(に) • (tsumini)