used to add to a negative statement, to disagree with a negative statement by someone else, or to answer no to a question:
It wasn't a good thing; on the contrary it was a huge mistake.
'I suppose your wife doesn't understand you.' 'On the contrary, she understands me very well.'
'Are they happy?' 'No, no, quite the contrary.'
something showing or saying the opposite:
Unless there is evidence to the contrary, we ought to believe them.
He continued to drink despite advice to the contrary.
the opposite of what has been said or suggested