noun
one copy; one volume
Counter for bound items like books, magazines, notebooks; 冊 counts volumes or copies.
この本を一冊ください。
Please give me one copy of this book.
彼は毎月一冊は小説を読む。
He reads at least one novel a month.
一部 is a more general counter for copies of documents, publications, or sets, while 一冊 specifically counts bound volumes.
一巻 can mean one volume of a multi-volume work, often used for series or scrolls, whereas 一冊 is a straightforward count of physical books.
Compound of 一 (いち, 'one') + 冊 (さつ, counter for books/volumes), with regular rendaku voicing of さつ to ざつ after いち, yielding いっさつ.