What does 到底 mean?
到底 is a Japanese adverb meaning “(cannot) possibly” in English. It is written as 到底 in kanji, とうてい in hiragana, and toutei in romaji. This word is part of JLPT N1 vocabulary.
Example sentence
あなたの話は到底真実だと思えない。
I can't possibly think your story is true.