underline vs underscore

underline and underscore both are nouns.

Word	Noun	Adjective	Verb	Adverb
underline	Yes	No	Yes	No
underscore	Yes	No	Yes	No

As nouns, underline and underscore are synonyms defined as:

underline and underscore: a line drawn underneath (especially under written matter)

As verbs, underline and underscore are synonyms defined as:

Other synonyms of underline include emphasise, emphasize.

As verbs, underline and underscore are synonyms defined as:

underline and underscore: draw a line or lines underneath to call attention to

underline (noun)	underscore (noun)
a line drawn underneath (especially under written matter)	a line drawn underneath (especially under written matter)

underline (verb)	underscore (verb)
give extra weight to (a communication)	give extra weight to (a communication)
draw a line or lines underneath to call attention to	draw a line or lines underneath to call attention to