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There is a general rule that for a kanji compound of the form 大＊, you tend to
read 大 using 音読み (タイ・ダイ) if ＊ is 漢語 and with 訓読み (おお) if ＊ is 和語. See e.g.
[this question on goo](https://oshiete.goo.ne.jp/qa/3353923.html) (in
Japanese). (Of course there are many exceptions, and this rule is not special
to 大---see [General guidelines for choosing 訓読み vs. 音読み in kanji
reading](https://japanese.stackexchange.com/q/43197/9199))

Are there any rules of thumb or broad etymological reasons for which 音読み to
use for 大 at the beginning of a kanji compound?

For instance, you typically read the following examples as タイ＊:

> 大木、大金、大量、大気、大変

and in these as ダイ＊

> 大事、大体、大地、大名、大学

One subjective impression I have is that if you have some 漢語, at least in the
case of 二字熟語, and modify it with 大 at the beginning that it is typically read
as ダイ, e.g., 大人気 or 大家族. (Compare this with 大使館, say, where the root word
seems to be 大使.)
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2018-10-10T11:18:33.220
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2018-11-08T17:57:32.593
9199
question
etymology readings
When 大 is read as たい versus だい？
The 音読み used for specific words varies based on when the word was borrowed
from Chinese. ダイ is the [呉音](https://en.wikipedia.org/wiki/Go-on) and タイ is
the [漢音](https://en.wikipedia.org/wiki/Kan-on). There's no hard rule for how
to tell which pronunciation to use.
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2018-11-08T17:57:32.593
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2018-11-08T17:57:32.593
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answer