straight off vs immediately

straight off and immediately both are adverbs.

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

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

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

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

straight off (adverb)	immediately (adverb)
without delay or hesitation; with no time intervening	without delay or hesitation; with no time intervening
	near or close by
	bearing an immediate relation