まさか can be used as a noun and adverb in Japanese.
Noun: upcoming events; An unexpected emergency. Nouns are often used after it.
Don't use it in some situations (it is useful when it is unexpected).
Adverb: I didn't expect it to be まさかがるとはわなかった. I didn't expect him to come.
When you are sick, it is impossible to come out and talk (say "come out" to the sick person).
Japanese is greatly influenced by Chinese. In Japanese, words with grammatical meaning all contain Chinese characters, and most of them are related to real meaning. Therefore, friends who usually know Chinese can understand the meaning of a short sentence even if they don't know Japanese. However, some words cannot be understood from the perspective of modern Chinese, because it is classical Chinese rather than vernacular Chinese that affects Japanese.
There are also some words that contain Chinese characters (and some are Japanese-made Chinese characters), but their meanings are quite different. For example, "time" (time, じかん) is not equal to time in Chinese, but represents a time period, and there are similar "years" (years, ねんかん).