adverb
generally; mostly; roughly; about
Adverbial use for approximations, overall tendencies, or when something is mostly true. Very common in everyday speech.
だいたいの人はその話を知っている。
Most people know that story.
仕事はだいたい終わった。
The work is mostly finished.
noun which may take the genitive case particle 'no'
Attributive use with の, meaning 'general' or 'rough', as in 大体の計画 (rough plan).
大体の予算を教えてください。
Please tell me the approximate budget.
noun
Noun use for the essential content or summary of something. Often used in phrases like 大体をつかむ (grasp the gist).
話の大体は理解できた。
I understood the gist of the story.
adverb
in the first place; to begin with; from the start
Adverbial use expressing that something is fundamentally the case or should have been obvious from the beginning. Often carries a tone of mild exasperation or emphasis.
だいたい、そんな計画がうまくいくはずがない。
In the first place, such a plan couldn't possibly work.