<p><strong>Adjective</strong></p><ul><li>happening, coming, made, or done quickly, without warning, or unexpectedly: a sudden attack.</li><li>Antonyms: gradual.</li><li>occurring without transition from the previous form, state, etc.; abrupt: a sudden turn.</li><li>Antonyms: gradual.</li><li>impetuous; rash.</li><li>Archaic: quickly made or provided.</li><li>Obsolete: unpremeditated.</li></ul><p><strong>Adverb</strong></p><ul><li>Literary: without warning; suddenly.</li></ul><p><strong>Noun</strong></p><ul><li>Obsolete: an unexpected occasion or occurrence.</li></ul>