Immediately means right now, with no delay at all. Come here immediately. The effect was immediate.
It sits at the strongest end of a scale that runs through soon, shortly and at once, and it is more formal than straight away, which is what people actually say. It also means directly in position or sequence: immediately behind the house, immediately after the war, with no gap between. That spatial use is common in writing and is often missed. Note the spelling, which has two m's and an e in the middle, and which is among the most misspelled adverbs in English.
1adverbimmediatelyAt once, with no delay.
“Ring me immediately if anything changes.”
synonyms: at once, instantly, straight away
2adverbdirectlyDirectly, with nothing in between.
“The shop is immediately opposite the station.”
Too few real examples of this word to estimate which sense is commonest.
immediately is a manner of timing.
Also accepted in games: instantly, at once
Middle English
immediatly
English, today
immediately
From Middle English immediatly, equivalent to immediate + ly.
Etymology from Wiktionary, CC BY-SA