一本 (ippon) means “one” | MotiTan Japanese Dictionary

More examples

鉛筆を一本使いました。en pitsu o ip pon tsuka i ma shi ta

I used one pencil.

Treats one long or cylindrical item as a single unit.

一冊ichisatsu: A counter for one book or other bound volume.
一個ikko: A counter for one separate object, especially a small or solid one.

棒状または筒状の物を一つ数えるときに用いる語。bō jō ma ta wa tsutsu jō no mono o hito tsu kazo e ru to ki ni mochi i ru go

一本 (ippon) is formed from 一 (ichi, "one") and 本 (hon, "base"); 本 extends from its basic sense of a stem or shaft to a counter for long objects.

A bottle is commonly counted as 一本 (ippon), whereas a book is 一冊 (issatsu), so 一本 does not generally mean one book.