prefixes - a few words have an honorific 「お」or「ご」 as a necessary prefix, right?

I just came a across the word 「お巡りさん」。While 「お巡り」 is a word, 「巡り」 is not. Likewise, 「ご飯」 is a word, but while 「飯」is a word, the reading changes to the 訓読み (めし)。This means that the 「ご」in「ご飯」is not window-dressing 美化語. The「ご」in「ご飯」is a necessary part of the word. In my opinion, 「お茶」 is in limbo. I've never heard 「茶」 spoken without an honorific 「お」、but 「茶」alone is officially in my dictionary。

Over time, 「お」or「ご」can become a necessary part of some words, right? Is this a documented part of Japanese grammar? (reference links would be welcomed). What are a few more words that have an honorific prefix, 「お」or「ご」, as a necessary part?

Answer

In language, a process is said to be productive if it can produce new words (or phrases, etc.). For example, in English, you can add un- to lots of words, so we say that un- affixation is a productive process. And in Japanese, affixing go- and o- to words is relatively productive.

But when a word can no longer be formed via a productive process in the modern language with a predictable meaning, we say that it's become lexicalized. In other words, it's become a single word, and it needs its own dictionary entry. You need a dictionary entry for disgruntled because you can't figure it out from dis- and gruntled in the modern language. Likewise, you need a dictionary entry for おやすみ, ごはん, and おにぎり because they've become single lexical words.

So yes, o- and go- can become a necessary part of a word, and the name for this process is lexicalization.