Both Uses

contrary
in
Much Ado About Nothing
(Auto-generated)

I would scarce trust myself, though I had sworn to the contrary, if Hero would be my wife.†
Scene 1.1
Question: why, an hour in clamour and a quarter in rheum: therefore is it most expedient for the wise,—if Don Worm, his conscience, find no impediment to the contrary,—to be the trumpet of his own virtues, as I am to myself.†
Scene 5.2 *

Definitions:

(1) (contrary as in: a contrary idea)
different (perhaps opposite or mutually exclusive)

In formal logic, contrary propositions or contrary arguments describe two things that cannot both be true. They might be described as mutually exclusive. For example, a pet cannot be both a cat and a dog. It doesn't need to be either, but if it is one, it cannot be the other. So the statement that a pet is a cat and the statement that the same pet is a dog, are contrary statements.
(2) (contrary as in: a contrary personality)
disagreeable -- typically in reference to someone's personality
(3) (contrary to as in: contrary to)
in opposition to

You could also think of this as meaning, despite, or in spite of, or in conflict with; but since a common meaning of contrary is opposite, you many find it easiest to think of contrary to as in opposition to.
(4) (on the contrary as in: on the contrary)
an expression used to intensify denial of an idea
(5) (to the contrary as in: to the contrary)
with an opposite or different effect; or something with an opposite or different effect
(6) (meaning too rare to warrant focus)