instant
n. countablen. a very short period of time that happens almost immediately. You use it to talk about something that occurs right away without any delay.
n. an infinitesimal or extremely brief point in time; a precise moment. Often used in prepositional phrases to indicate immediate action or occurrence.
The light changed in an instant.
For an instant, the witness hesitated before identifying the suspect in the courtroom.
The legal implications of the contract became clear the instant the signature was applied, binding both parties to the terms immediately and without further recourse.
From Middle English instant (“infinitely short period of time”), from Old French instant (“assiduous, at hand”, adjective), from Latin īnstāns, īnstantis (“present, pressing, urgent”, literally “standing near”), present active participle of īnstō (“to stand upon, be nearby”), from in- (“after”) + stō (“to stand”). Compare Old English instede (“immediately, on the spot, at once”). More at in, stand.
From French instant and Middle English instant, both from Old French, from Latin instans (“standing by, being near, present, also urgent, importunate”), present participle of instō (“to stand upon, press upon, urge, pursue, insist”), from in (“on, upon”) + stō (“to stand”); see state.
Ultimately from Latin īnstāre; its precise evolution is uncertain. OED hints at (unattested) Middle French *instanter.
Commonly used in the prepositional phrase 'in an instant' or as a conjunction in 'the instant that'.
at the instantin an instantWhen describing something happening very quickly, 'in' is the standard preposition; 'at the instant' is usually followed by 'of' to mark a specific point in time.