to reduce the weight of (something)

to relieve (somebody's mind) of a burden

to make (something) less wearisome

More company increases happiness, but does not lighten or diminish misery — Thomas Traherne

to make (something) less serious or more cheerful

to make or become lighter or less burdensome

to make or become less serious or more cheerful

said of a mood, etc: to become less serious or more cheerful

to make (a place) light or bright

to make (a colour, hair, etc) lighter or paler

to grow lighter; to brighten

to discharge flashes of lightning