forthwith vs instantly

forthwith and instantly both are adverbs.

Word	Noun	Adjective	Verb	Adverb
forthwith	No	No	No	Yes
instantly	No	No	No	Yes

As adverbs, forthwith and instantly are synonyms defined as:

forthwith and instantly: without delay or hesitation; with no time intervening

Other synonyms of forthwith include at once, directly, immediately, like a shot, now, right away, straight off, straightaway.

forthwith (adverb)	instantly (adverb)
without delay or hesitation; with no time intervening	without delay or hesitation; with no time intervening
	without any delay