Reading of prefix 大


While reading, I'm finding difficult to understand how to read an initial 大,
since it can be read だい (大好物), たい (大使館), おお (大蔵省).

When I can find the word on a dictionary it's not a big problem, I can just
check, but when dictionaries don't list it I have no idea how I should read
it; for example, 大集団 should be だいしゅうだん? おおしゅうだん? It's the same? I tried Jisho
and Weblio, and I wasn't able to find it.

IME gives 大集団 for both pronunciations, but I know it also makes up for errors
to some extent, so I can't be sure if both readings are right, or IME is just
making up for a mistake in typing.

[As far as I
found](https://japanese.stackexchange.com/questions/62095/when-%E5%A4%A7-is-
read-as-%E3%81%9F%E3%81%84-versus-%E3%81%A0%E3%81%84), there are no hard rules
in this regard, but since in that answer the answerer speaks about when the
word was borrowed from Chinese, and since Japanese speakers have to read it
somehow when speaking the word I was wondering if there is some rule about how
to read it when used as a prefix of other words, rather than using a word that
already contains it.

I know the opening examples aren't examples of prefix だい, I just bring them to
exemplify the different readings; my doubt is that, given that as far as I
know a general (i.e., not just prefix) initial 大 doesn't follow any hard
pronunciation rule, is there some way to know how it should be read when used
as prefix, like in 大集団?




The basic rule is that だい attaches to kango (words with on-reading) and
gairaigo (written in katakana), while おお attaches to wago (words with kun-
reading). Easy examples are:

  * 大画面: だいがめん
  * 大都市: だいとし
  * 大アルカナ: だいあるかな
  * 大ブリテン王国: だいぶりてんおうこく
  * 大騒ぎ: おおさわぎ
  * 大笑い: おおわらい

大集団 follows this basic rule as well, so it's だいしゅうだん. When a word is not in a
dictionary with a 大, I think you can follow the basic rule.

However, there are counterexamples where おお attaches to on-readings:

  * 大喧嘩: おおげんか
  * 大火事: おおかじ
  * 大騒動: おおそうどう or だいそうどう
  * 大地震: おおじしん or だいじしん
  * 大人数: おおにんずう or だいにんずう
  * 大風呂敷: おおぶろしき (風呂敷 is a mixed on-kun compound)

It's hard to explain why. Some say these are well nativized words which no
longer has a good wago equivalent, but all you can do practically is remember
them individually.




The basic rule is that だい attaches to kango (words with on-reading) and
gairaigo (written in katakana), while おお attaches to wago (words with kun-
reading). Easy examples are:

  * 大画面: だいがめん
  * 大都市: だいとし
  * 大アルカナ: だいあるかな
  * 大ブリテン王国: だいぶりてんおうこく
  * 大騒ぎ: おおさわぎ
  * 大笑い: おおわらい

大集団 follows this basic rule as well, so it's だいしゅうだん. When a word is not in a
dictionary with a 大, I think you can follow the basic rule.

However, there are counterexamples where おお attaches to on-readings:

  * 大喧嘩: おおげんか
  * 大火事: おおかじ
  * 大騒動: おおそうどう or だいそうどう
  * 大地震: おおじしん or だいじしん
  * 大人数: おおにんずう or だいにんずう
  * 大風呂敷: おおぶろしき (風呂敷 is a mixed on-kun compound)

It's hard to explain why. Some say these are well nativized words which no
longer has a good wago equivalent, but all you can do practically is remember
them individually.

