I'm a beginner so soory for my English. I don't know and couldn't find which one is right on the internet. Is"(the) most greatest" used by people? Or like, is it right to use that? I saw this in a book. Although I say "(the) greatest" normally, just wanted to make sure. Thank you!
There are two ways of expressing this:
- the most great
- the greatest
Either of the above phrases is possible. Most great is not wrong, but the more common, and shorter, is simply greatest.
Only one thing (or group of things) can be the greatest. Combining the two words to say most greatest is redundant and, while understandable, would be considered wrong.
You are right that "the greatest" is correct.
This article explains about comparatives and superlatives. Some adjectives (as the article says, mainly shorter ones) form their comparative and superlative with suffixes (-er and -est), and some (longer words) use more and most.
"The most beautiful island in the world."
"The greatest story ever told."
There are a few exceptions (e.g. good-better-best), but using both most and -est together is not correct in standard English.
If you saw "the most greatest" in a book, perhaps it was dialog spoken by a child, or some other example of purposely incorrect language. That is an expression we don't normally use in English.