A warden has less authority. I suspect this is general as wardens can be private. Any organisation can appoint a warden: it is a roll. It has authroity only as empowered by whoever appointed it for wahtever purpose.
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Generally, "cop" means police, working for some form of justice department with authority delegated by the government, be it local or federal.
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Here city councils appoint wardens.
"Meter maid" would be considered derogatory for either gender, here. Parking enforcement officer? Parking warden?