Missing 「ん」in 大文字 (Uppercase Letters, vocabulary)

[rowot]

So I stumbled upon 大文字 in my lessons, and the reading of this word, as described in the lesson, is an exception. 大 uses the kun’yomi reading, and 文字 both use the on’yomi readings. However, it seems that the reading of 文 is just も, not もん, despite the fact that the on’yomi reading for it is もん. The question is: why? Is this just another exception? In the lesson itself it only says that 大’s reading is an exception, there is nothing about 文’s reading. I think I’ve seen similar oddities in vocabulary before, but only now have I decided to ask this question.

[seanblue]

文字 is usually read もじ, not もんじ. Since you already learned 文字 two levels before 大文字, they probably don’t need to explain that completely. But it’s a little misleading to say “everything else is just on’yomi” since the も for 文 is an exception.

If you email them to explain this, they’ll probably update the explanation to reference back to 文字.

[rowot]

So essentially the reason why 大 uses kun’yomi reading is that 大文字 is actually 2 separate words (literally — big letter) or something like that?

[Leebo]

I don’t think you can necessarily say there’s a “reason” for it. Exceptions exist in various ways, so even if there was a reason it would get violated by other words. The reading だいもんじ also exists in the dictionary. I’ve never seen it before, but it makes sense why it exists.

[Myria]

だいもんじ usually refers to the big letters lit up on the mountains around Kyoto in August, in a festival called 五山送り火 (Gozan no Okuribi). So while the reading exists, it’s only used for this rather special case.

[TamanegiNoKame]

I am always amazed at the amount of random, awesome detail that people on this forum know about different niches of the Japanese language.