Of a book or document: lengthy, voluminous; having a large bulk or many pages.
あの作家の新刊は大部で持ち運ぶのが大変だ。
That author's new book is voluminous and hard to carry.
学会に提出された報告書は大部で細かいデータが載っている。
The report submitted to the conference is lengthy and contains detailed data.
大部の書類は電子化して保存したほうが管理しやすい。
It's easier to manage voluminous documents if you digitize and store them.
Mostly; to a large extent; considerably; an adverb meaning 'quite' or 'much' (similar to だいぶ).
だいぶ寒くなってきたから、コートを出した。
It's gotten quite cold, so I took out my coat.
仕事は大部片付いた。あとは最終チェックだけだ。
Most of the work is done. Only the final check remains.
彼は日本語が大部上達したね。
He's improved his Japanese quite a lot.