“immediately”

Without delay or hesitation; at once.

“The general ordered the troops to withdraw forthwith before dawn broke over the ridge.”

Best for: Formal writing, legal documents, or dialogue seeking an authoritative tone.

With the greatest possible speed or urgency.

“She packed her bags posthaste and was out the door before he finished his sentence.”

Best for: Narrative prose or casual elevated writing; carries a slightly dramatic, old-world flair.

At this very instant; immediately and without any interval of time.

“The judge demanded instanter compliance, and the courtroom fell silent.”

Best for: Legal or archaic formal contexts; delivers a sharp, non-negotiable urgency.

Quickly and without wasting time.

“Get the engine running pronto — they're already two blocks ahead.”

Best for: Casual speech, snappy dialogue, or punchy action writing.

Immediately; right away, borrowed directly from French meaning 'all in sequence.'

“She expected the champagne delivered tout de suite, not sometime after midnight.”

Best for: Stylish or ironic registers; lends cosmopolitan flair to a scene or character.

In an archaic sense, immediately and without restraint of time.

“Upon reading the letter, he left incontinent, vanishing into the fog-wrapped street.”

Best for: Rare literary or historical fiction contexts; startles readers pleasantly with its unexpected meaning.