Adjective instant has 3 senses
  1. instantaneous, instant - occurring with no delay; "relief was instantaneous"; "instant gratification"
    Antonym: slow (indirect, via fast)
  2. instant, inst - in or of the present month; "your letter of the 10th inst"
    Antonym: future (indirect, via past, present)
    Antonym: past (indirect, via present, future)
  3. clamant, crying, exigent, insistent, instant - demanding attention; "clamant needs"; "a crying need"; "regarded literary questions as exigent and momentous"- H.L.Mencken; "insistent hunger"; "an instant need"
    Antonym: beseeching (indirect, via imperative)
,Noun instant has 2 senses
  1. blink of an eye, flash, heartbeat, instant, jiffy, split second, trice, twinkling, wink, New York minute - a very short time (as the time it takes the eye blink or the heart to beat); "if I had the chance I'd do it in a flash"
    --1 is a kind of moment, minute, second, bit
  2. moment, minute, second, instant - a particular point in time; "the moment he arrived the party began"
    --2 is a kind of point, point in time
    --2 has particulars:
     climax, culmination; eleventh hour, last minute; moment of truth; moment of truth; pinpoint; time; psychological moment
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