Circular, Round, Spherical
い adjective
With an い on the end, you can guess that this word is an い-adjective. What is the adjective version of the kanji 丸? "Circle" becomes circular, spherical or round. This, compared to another similar word (円), is more general purpose and can be used with 3D spherical objects as well.
まるい
This word uses the reading you learned for the kanji 丸, though you'll need to tack the い onto the end too.
丸いボールがほしい。
I want a round ball.
このレストランには丸いフルーツしかありません。
This restaurant only serves round-shaped fruit.
この玉、ちょっと丸すぎませんか？
Isn't this ball a bit too round?