A British spelling ending added to verbs (like 'realise,' 'organise'), equivalent to the American '-ize' ending.
From Greek '-ize,' but the '-ise' variant became standard in British English during the 19th century. Both ultimately derive from Greek '-izein' meaning 'to make or treat as.'
The British '-ise' versus American '-ize' debate is so intense that some style guides will 'penalise' you for using the wrong one—even though dictionaries accept both!
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