wheelhorse
wheel.horse \'hwe-(*)l-.ho.(*)rs, 'we-(*)l-\ n 1: a horse in a position nearest the wheels in a tandem or similar arrangem ent 2: a steady and effective worker esp. in a political body
Webster's English Dictionarywheel.horse \'hwe-(*)l-.ho.(*)rs, 'we-(*)l-\ n 1: a horse in a position nearest the wheels in a tandem or similar arrangem ent 2: a steady and effective worker esp. in a political body