J44xm said:
WWWJDIC's example sentences do not clearly (if at all) distinguish between levels of politeness. Both words are simply listed as "today."
You're not making the best use of them. In fact did you actually _look_ at the example sentences? It sounds from "both words are simply listed as" that you're talking about the dictionary entries.
If I try the example sentences the first thing I find is that there are (total)
17 sentences for 本日 and
several hundred* for 今日. So you already know one important difference between 本日 and 今日.
If you look at the actual content of the example sentences ...
本日
恐れ入りますが、本日は満席です。
Sorry, we're full today.
首相は本日声明を発表する予定です。
The Prime Minister is to make a statement today.
ご主人は本日お見えになるでしょう。
I believe he'll be with us today.
本日のランチの内容はなんですか。
What are you serving today.
本日の特別料理について説明します。
Let me tell you about our special.
本日は御搭乗頂きありがとうございます。
Welcome aboard!
本日はお乗りいただきありがとうございます!
Welcome aboard!
病気のために本日は伺うことができませんでした。
On accounts of illness, I couldn't call on you today.
あいにくですが本日は予約でいっぱいです。
I'm sorry, today is fully booked.
It's obvious that all the examples are very polite and generally 'humble'. If you just look for
"what word is 本日 translated as" you've missed most of the point of example sentences.
* In fact 1191