1 at once, instantly, instantaneously, promptly, right away, right now, without delay, unhesitatingly, without hesitation, forthwith, this instant, directly, in a wink, in a second, in a minute, tout de suite, instanter, Chiefly Brit straightaway or straight away, Colloq pronto, in a jiffy, in two shakes of a lamb's tail, before you can say 'Jack Robinson', at the drop of a hat:
Come here immediately. I shall be there immediately.
2 directly, closely, intimately:
These reactions are immediately concerned with the temperature.
3 when, as soon as, the moment (that), Brit directly:
Immediately he heard the news, he hurried to her side.