Informal contraction of 'is not', commonly used in casual speech and writing.
Modern English contraction formed by combining 'is' and 'not' with an apostrophe marking the omitted letters. This type of contraction became standardized in English during the 17th-18th centuries as written language began reflecting spoken patterns.
Contractions like 'isn't' are fascinating because they show how written language constantly evolves to match how we actually speak - they were once considered improper but are now essential for natural-sounding English!
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