I
adjective
1
BAD : People have opposite opinions about this matter.
GOOD : People have different opinions about this matter.
BAD : The Americans I met were opposite to what I had imagined.
GOOD : The Americans I met were very different from what I had imagined.
BAD : My own country and the USA are totally opposite of each other.
GOOD : My own country and the USA are totally different (from each other).
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Use opposite and the opposite of only when you mean that two things are as different as it is possible to be: 'I thought that the medicine would make him sleepy, but it had the opposite effect.' 'The opposite of long is short .' 'The two men went off in opposite directions.' (= one went to the left and one to the right)
To describe people's opinions, life styles, ways of thinking etc, the usual word is different : 'These two schools of thought are completely different.'
2
BAD : The opposite woman was knitting a cardigan.
GOOD : The woman opposite was knitting a cardigan.
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When opposite means 'facing the speaker or the person/place being talked about', it comes immediately after the noun: 'The house opposite is also for sale.'
II
preposition
BAD : On the wall opposite to the door, there was a large painting.
GOOD : On the wall opposite the door, there was a large painting.
BAD : The phone booths are opposite of the tube station.
GOOD : The phone booths are opposite the tube station.
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One thing is opposite another thing (WITHOUT to/of ): 'The nearest bus stop is opposite the bank.'