straight off vs forthwith

straight off and forthwith both are adverbs.

Word	Noun	Adjective	Verb	Adverb
straight off	No	No	No	Yes
forthwith	No	No	No	Yes

As adverbs, straight off and forthwith are synonyms defined as:

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

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

straight off (adverb)	forthwith (adverb)
without delay or hesitation; with no time intervening	without delay or hesitation; with no time intervening