Both words refer to acts of the mind that can be objectively true or false. But there is an important difference.
False knowledge is self-contradictory.
If a statement is false, it does not express our knowledge. But a statement of opinion can be either true or false. To take account of this difference between knowledge and opinion, it is necessary to regard opinions as only probably true or false, whereas knowledge is true beyond the shadow of a doubt. It has certitude. Self-evident truths, truths the opposites of which are unthinkable, are invariant truths.