lighten
/ˈlaɪtn; `laɪtn/ v[I, Tn]
1 (cause sth to) become lighter in weight （使某物）变轻
lighten a burden, cargo, pack, etc 使负担、 货物、 包装等变轻.
2 (cause sth to) be relieved of care or worry （使某事物）令人放心, 解除忧虑
My mood gradually lightened. 我的心情慢慢轻松起来.
lighten sb's duties 减轻某人的责任.