adjective
1
BAD : The third paragraph of the essay is not appropriate.
GOOD : The third paragraph of the essay is not relevant.
BAD : Will you please send me all the appropriate information?
GOOD : Will you please send me all the relevant information?
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appropriate = suitable in a particular situation: 'Once we know more about the cause of the problem, we can take appropriate action.' 'To offer them more money at this stage would not be appropriate.'
relevant = having a clear connection with what you are doing or talking about: 'I'll try to answer any questions, as long as they are relevant.' 'You cannot enter the country unless you have obtained all the relevant documents.'
2
BAD : Some bottles are not appropriate for recycling.
GOOD : Some bottles are not suitable for recycling.
BAD : She is clearly the most appropriate person for the job.
GOOD : She is clearly the most suitable person for the job.
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Appropriate and suitable have similar meanings and are sometimes interchangeable: 'We're still waiting for a suitable/an appropriate moment to break the news to them.'
When you mean 'having the necessary qualities, skills etc, the usual word is suitable : 'The hotel isn't suitable for families with children.'