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To decide definitively that something will or can possibly happen. (Used especially—and somewhat redundantly—in the phrase "not ruled in or ruled out.") Look, nothing has been ruled in or ruled out at this stage, so we just have to wait until the doctors have more information to work with. We'll neither rule in nor rule out the possibility of a shakeup in management if this branch's profits continue to fall.
See also: rule
To be the best; to be the most dominant or in control; to be the most favoured or supported by the public. (Used originally in relation to football clubs or local gangs in graffiti writing.) Primarily heard in UK. Someone had come with a can of black spray paint and crossed out the big "Leeds Rules OK" that was painted on the side of the school. But in this part of the country, the conservatives rule OK with almost no opposition.
rule with a rod of iron
To rule, govern, or control a group or population with complete power over all aspects of life, work, etc. Primarily heard in UK, Australia. He rules with a rod of iron, and moves swiftly to gain control over any entity that is not already in his grasp. She has ruled this company with a rod of iron for three decades, and it's going to be difficult for her to let go of control.