Football’s Greatest Clubs

How does one go about measuring greatness in football? I mean real, obvious, blatant greatness; that rarest of qualities. Today "greatness" is such a woolly, over-used term that sometimes we lose its meaning and start labeling all sorts of mundane, workaday things as "great". The evolution of language has distilled its meaning, reduced its potency, but we still know greatness when we see it.