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Avoid imformal words in formal writing

Words or expressions labeled Informal or Colloquialin college dictionaries are standard English and are used by speakers and writers every day. These words are thus appropriate in informal writing especially in dialouge. But informal words or expressions are usually inappropriate in formal expository compositions. In formal writing, use instead the general English vocabulary, the unlabeled words in your dictionary.

Informal In class the teacher gave a definition of polyunsaturated, but I didn't get it.

General In class the teacher gave a definition of polysaturated, but I didn't understand it.

As a rule, contractions are avoided in formal writing. Contracted forms like
won't, there's, or she's are normally writtne out: will not, there is or there has, she would or she had.

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