Word explanation

[amna]

can we use word decorous instead of correct in conversation or it is only for writing pl explain.

[Alan]

These are two adjectives that are slightly different in use. Correct can be simply right as in the correct answer or it can mean right in the sense of proper as accepted by society. Decorous on the other hand means appropriate in terms of behaviour with regard to good taste and is obviously formed from the noun decorum, referring to what society expects from its citizens. You could use it to mean refined/elegant. As an adjective it can refer to a certain style of writing but it is not used as right with regard to right answer. As for both words, they can be used in spoken and written language.
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English as a Second Language
You can read my ESL story Prepositions