Almost always written purely in hiragana, まさか
is a combination of まさ, a 名詞（めいし） (noun) meaning ‘precise’, or ‘exact’, and the 副助詞（ふくじょし） (adverbial particle) か. In modern Japanese, まさか
is thought of as a single 副詞（ふくし） (adverb) meaning ‘it can’t be true’, ‘no way’, or ‘don’t tell me’.
As it is treated primarily as an adverb, まさか
will most often appear at the beginning of a sentence, before some statement about what the speaker is shocked/surprised about.
I never would have believed that you also came to this gym.
Don’t tell me that he is the captain!
まさ comes from 正（まさ）, meaning ‘precise’ or ‘actual’. However, this noun is very rarely used in modern Japanese. まさに is an adverb used to mean ‘precisely’, while まさか
is another adverb used to mean ‘no way!’. However, the literal meaning of まさか
is closer to ‘is it true?’, or ‘is it actually?’, due to か’s role in creating questions.
I didn't wait at all. I actually just arrived now.
Is it actually true that Lia is going back to France?