1A prefix meaning large/big/great/major/important (often denoting large size or degree). Pronunciation varies by word (おお／だい／たい).
今日は大雨で外出できない。
It's pouring today, so we can't go out.
会場で大声を出してはいけない。
You must not shout loudly in the venue.
大事な書類は忘れないで持ってきてください。
Please don't forget to bring the important documents.
2Indicating older or senior (seen in certain words and often archaic or limited to fixed expressions).
『大姉』は年上の姉を指す古い言い方だ。
'大姉' is an old expression referring to an elder sister.
古い文献には『大兄』のような表現が見られることがある（年上の兄を指す）。
Old texts sometimes contain expressions like '大兄', referring to an elder brother.
3Used as a prefix meaning final, ultimate, or climactic (e.g., 大団円 for a grand finale).
映画は大団円で終わり、観客は拍手した。
The film ended in a grand finale, and the audience applauded.
プロジェクトは最後に大成功を収め、大団円となった。
The project achieved great success in the end and concluded on a high note.
4A prefix meaning rough, broad, or general (indicating an approximate or overall sense rather than detail).
計画はまだ大まかな段階だ。詳細はこれから詰める。
The plan is still in a rough stage. We'll work out the details later.
彼の説明は大雑把で、具体的な数字がない。
His explanation was rough and lacked concrete numbers.