1A circle; anything round or circular (the shape or symbol '○').
紙に丸を描いて名前の横に付けておいた。
I drew a circle on the paper and put it next to the name.
この公園には丸い噴水がある。
There is a circular fountain in this park.
2The entirety or wholesomeness of something; used to mean whole or complete (e.g., 'entirely', 'whole').
リンゴを皮ごと丸ごと食べた。
I ate the apple whole, skin and all.
会社は丸一年かけてプロジェクトを完成させた。
The company completed the project over the course of a full year.
3Slang for money; dough (colloquial).
あいつは丸をたくさん持っているらしい（俗語）。
Apparently he has a lot of money (slang).
新しいビジネスで丸を儲けた。
He made a lot of money with the new business.
4An enclosure inside a castle's walls — a bailey or inner ward (used in castle terminology).
本丸は城の最も重要な建物がある場所だ。
The honmaru (main bailey) is where the castle's most important buildings are located.
5In Kansai dialect, a term sometimes used for the soft‑shelled turtle (regional usage).
関西では昔、『丸』でスッポンを呼ぶことがあったらしい（方言）。
Apparently in Kansai people used to call soft‑shelled turtles 'maru' (dialect).
6A suffix used in ship names, people’s names (especially infants), names of swords, instruments, dogs, horses, etc.; commonly seen as '‑maru' at the end of such names.
昔の商船には『二葉丸』のように『丸』が付く名前が多かった。
Old merchant ships often had names ending with '‑maru', like 'Futabamaru'.
幼い子の名前に『丸』を付ける習慣が昔はあった。
There used to be a custom of adding 'maru' to a young child's name.