adv. 25B6; adverb
it was necessary to make a decision immediately : STRAIGHT AWAY, at once, right away, instantly, now, directly, promptly, forthwith, this/that (very) minute, this/that instant, there and then, here and now, without delay, without further ado, post-haste; quickly, as fast as possible, speedily, as soon as possible, a.s.a.p.; informal pronto, in double-quick time, pretty damn quick, p.d.q., toot sweet; archaic instanter, forthright.
I sat immediately behind him : DIRECTLY, right, exactly, precisely, squarely, just, dead; informal slap bang; N. Amer. informal smack dab.