A bully is someone who torments and taunts others, with the term most often associated with older children "picking on" younger ones, with this relationship common in siblings.
Captain Jean-Luc Picard once told his brother Robert that when they were growing up, Robert had been a bully. Robert responded that he had enjoyed bullying Jean-Luc with the statement resulting in the two having a fight. (TNG: "Family")
Jake Potts once bullied his brother Willie with deadly consequences. Jake tricked Willie into thinking Willie had killed him in a laser duel and Willie, in terror, fled into an alien forest on Ogus II and ate a deadly cove palm. Willie was later rushed to a starbase for emergency medical care. (TNG: "Brothers")