lighten
v.
1
"to make less heavy," figuratively "to make cheerful," mid-14c., from light, adj.1 + -en(1). Related: Lightened; lightening.
2
"shed light upon, illuminate, brighten," early 14c., from light, n. -en(1). Meaning "to grow brighter" is late 14c. Of faces, expressions, etc., from 1795. Related: Lightened; lightening.