In British English and most other varieties of English from outside North America, practice is the noun, and practise is the verb. There is no such distinction in American English, where practice is both a noun and a verb. Canadian English also favors practise as the verb, but practice appears with relative frequency (about a third as often as practise).
The participle forms of practise are practised and practising, and the simple-present inflection is practises.
Examples
These British and Australian publications favor practise as a verb and practice as a noun:
In golf, Ben Hogan, one of the game’s greats, was known to practise more than any of his contemporaries and is said to have “invented practice”. [Independent]
We try to look at making practice more efficient, ways of practising more under pressure … [The Sun]
Others escaped to the outer edges of Australian territory, into Papua New Guinea or Antarctica, where they were allowed to practise medicine. [Sydney Morning Herald]
And these American publications use practice as both a noun and a verb:
The natural grass practice fields behind Halas Hall have been ripped up and a crew is working to install new surfaces right now. [Chicago Tribune]
Yet Wall Street, for its first 200 years, remained a WASP preserve, where prejudice was practiced openly. [Daily Beast]
We’re used to seeing Raylan as a clear-thinking man of action, practicing Old West-style justice in a contemporary setting. [AV Club]
