directly vs straightaway

directly is not a noun while straightaway is a noun.

Word	Noun	Adjective	Verb	Adverb
directly	No	No	No	Yes
straightaway	Yes	Yes	No	Yes

As adverbs, directly and straightaway are synonyms defined as:

directly and straightaway: without delay or hesitation; with no time intervening

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

directly (noun)	straightaway (noun)
	a straight segment of a roadway or racecourse

directly (adjective)	straightaway (adjective)
	performed with little or no delay

directly (adverb)	straightaway (adverb)
without deviation	without delay or hesitation; with no time intervening
in a forthright manner; candidly or frankly
without anyone or anything intervening
without delay or hesitation; with no time intervening