noun
1
BAD : The scholarship provided me with my first occasion to travel overseas.
GOOD : The scholarship provided me with my first opportunity to travel overseas.
BAD : I never had occasion to take the Proficiency examination.
GOOD : I never had a chance to take the Proficiency examination.
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occasion = the time when an event happens: 'I've been to Rome on several occasions.' (= several times)
opportunity = a time when it is possible to do something that you want to do: 'The meeting on Tuesday will be a good opportunity for you to make some new contacts.' 'She has considerable ability and should be given more opportunity to use it.'
chance = an informal word for 'opportunity': 'If I had the chance, I'd like to be an airline pilot.' 'I've been so busy this morning I haven't had a chance to sit down.'
2
BAD : I remember that in the last occasion he had a very bad cold.
GOOD : I remember that on the last occasion he had a very bad cold.
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on a particular occasion (NOT in ): 'I am honoured that you have invited me to join you on this special occasion.'