Synonym of ‘Unusual’ is:

A synonym is a word or phrase that means exactly or nearly the same as another word or phrase in the same language. The word 'Unusual' describes something not common, ordinary, or expected.

• Extraordinary is the correct synonym because it means beyond what is ordinary or usual; remarkably good or impressive, perfectly aligning with the meaning of 'unusual'.
• Ordinary is incorrect as it is an antonym, meaning common or regular.
• Usual is incorrect as it is also an antonym, meaning customary or normal.
• Routine is incorrect as it implies a regular, unvarying procedure, which is the opposite of unusual.