They all mean something like **an instant** or **a moment**.

  * When are they (and when are they not) interchangeable?
  * Is any more (in)formal/literary than the others?
  * Do they represent the same amount of time? 
    * My gut says that 一瞬 is the quickest ([like [電光石火]{でん・こう・せっ・か}](https://japanese.stackexchange.com/q/4243/78)) and that 一刻 can be a longer "moment" (like 即席ラーメン or, "Can you answer a quick servey? It'll only take a **moment** of your time.").
    * _I've_ never heard (一)刹那 used in real life, so I have no basis for comparison.
CC BY-SA 4.0
2018-08-31T16:18:09.000
61222
2018-09-01T08:27:15.183
78
question
word-choice words nuances synonyms
What is the difference [一瞬]{いっ・しゅん}, [一刻]{いっ・こく}, and [(一)刹那]{(いっ・)せつ・な}
* 刹那 is clearly more literary than the others. It's originally a Buddhism term.
  * As a no-adjective, 一瞬の and 刹那の are mostly interchangeable (except that the latter being literary and thus emphatic/dramatic)
  * As a conjunction-like noun (?), ～した刹那 is interchangeable with ～した瞬間.
  * As a na-adjective, [刹那的](https://eow.alc.co.jp/search?q=%E5%88%B9%E9%82%A3%E7%9A%84&ref=sa) means "ephemeral" (negative); 瞬間的 is "instant"; 一瞬的 makes no sense.
  * 刻 is originally a unit of time that roughly corresponds to 30 minutes. Today, 一刻 is used almost exclusively in idioms (一刻を争う, 一刻一刻(と), 一刻の猶予もない, etc), and I don't know how to use 一刻 with ラーメン. 一刻 basically refers to a longer time than 一瞬/刹那. In other words, 一瞬/刹那 roughly means "less than a second" or "less than a minute" at most, whereas 一刻 roughly means "less than an hour".
CC BY-SA 4.0
2018-09-01T07:11:52.883
61239
2018-09-01T08:27:15.183
2018-09-01T08:27:15.183
5010
5010
61222
answer