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perfectly round; perfectly circular
子猫の真ん丸い目がとても愛らしかった。
The kitten's perfectly round eyes were very adorable.
夜空に浮かんだ満月は真ん丸かった。
The full moon floating in the night sky was perfectly round.
手作りの団子はあまり真ん丸くない。
The handmade dumplings aren't very perfectly round.