to mark with a line or lines underneath; underline, as for emphasis.

to stress; emphasize

The recent tragedy underscores the danger of disregarding safety rules.

a line drawn beneath something written or printed.

music for a film soundtrack; background for a film or stage production.

verb

accent , accentuate , call attention to , caption , draw attention to , feature , give emphasis , highlight , indicate , italicize , mark , point to , stress , play up , point up , underline , emphasize , heighten