underscore vs underline

underscore and underline both are nouns.

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

As nouns, underscore and underline are synonyms defined as:

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

As verbs, underscore and underline are synonyms defined as:

Other synonyms of underscore include emphasise, emphasize.

As verbs, underscore and underline are synonyms defined as:

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

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

underscore (verb)	underline (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