(a.) Immediately; instantly; at once; as, he left instanter.

PDQ amain at flank speed at once by forced marches cursorily decisively directly double-quick expeditiously fast feverishly flat-out forthwith furiously hand over fist hand over hand hastily hell for leather hell-bent hell-bent for election helter-skelter hotfoot hurriedly hurry-scurry immediately in double time in double-quick time in high in high gear in no time in passing in seven-league boots instanter instantly lickety-cut lickety-split on the double on the instant on the run on the spot pell-mell post posthaste pretty damned quick promptly pronto quick quickly rapidly right away right off slapdash smartly snappily speedily straightaway straightway subito summarily superficially swiftly trippingly under forced draft whip and spur with a rush with all haste with all speed with dispatch with giant strides with haste with rapid strides with speed without delay without further delay