What does jiji mean in Japanese?

My father and his siblings called their dad that and one of my Japanese teachers said it was a derogatory way to say old man. None of the kids spoke Japanese but I know my grandfather did but since his parents were the ones who left Japan maybe he didn't know it was derogatory? Or maybe it means something... show more My father and his siblings called their dad that and one of my Japanese teachers said it was a derogatory way to say old man. None of the kids spoke Japanese but I know my grandfather did but since his parents were the ones who left Japan maybe he didn't know it was derogatory? Or maybe it means something else-I'm just not sure but it bugs me.
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