Here are some options depending on the context:
* おてんば (otenba): This is the most common and closest equivalent, literally meaning "wild" or "unruly." It describes a girl who is energetic, playful, and tomboyish.
* 男勝り (otokomasari): This means "like a man" and implies a girl who is strong, assertive, and doesn't conform to traditional feminine stereotypes.
* ボーイッシュ (boish): This is a loanword from English, meaning "boyish," and is commonly used to describe a girl's style, but can also be used to describe her personality.
* 活発な女の子 (katsubatsu na onna no ko): This literally means "active girl" and is a more general term that can encompass various personality traits, including tomboyish behavior.
Ultimately, the best way to convey the meaning of "tomboy" in Japanese depends on the specific context and the nuance you want to express. It's always helpful to provide more information about the situation when asking for translation.