1An adverb meaning 'generally,' 'roughly,' or 'approximately' — used to express an overall estimate without going into detail.
だいたいの時間を教えてください。
Please tell me the approximate time.
だいたい終わったから、片付け始めよう。
It's almost finished, so let's start tidying up.
その計画はだいたい問題ないと思う。
I think that plan is generally fine.
2Used in the form 「大体の〜」 to mean a general or rough version of something, as opposed to the fine details.
まず大体の計画を立ててから詳細を詰めよう。
First make a rough plan, then work out the details.
大体の見当はついたが、確認が必要だ。
I have a rough idea, but it needs to be checked.
3A noun meaning the outline or gist of something — the overall content, excluding minor details.
会議の大体をメモにまとめておいてください。
Please summarize the main points of the meeting in a memo.
論文の大体が分かったら、序章を書き始めよう。
Once you understand the gist of the paper, start writing the introduction.
4An adverb used at the start of a statement to point out a fundamental issue, often with a critical or exasperated tone, similar to 'in the first place.'
だいたい、彼が来るかどうか確認してから進めよう。
First of all, let's confirm whether he's coming before we proceed.
だいたい、謝るべきは彼のほうだと思う。
To begin with, I think he's the one who should apologize.
だいたい、こんな時間に電話してくるのが非常識だ。
In the first place, it's inconsiderate to call at this hour.