"おねジジ" (onejiji) is a Japanese slang term that combines "おね" (one), an abbreviation of "お姉さん" (onee-san), meaning "older sister," and "ジジ" (jiji), which is a playful and affectionate term for "叔父さん" (oji-san), which means "grandfather" or "old man."

"お姉さん" (onee-san) typically refers to an older sister. However, it can also be used more broadly to refer to young women or women who are older than the speaker but still relatively younger compared to an old man.