The word practice originated from the Greek word "prassein," morphed into "praktikos," then "practicus" and finally "practizare" before it entered the English language in the 15th century as the verb "practise." In the 16th century, the noun form "practice" was introduced. Although the majority of American English is derived from British English, the word practise was not assimilated into the American language as the verb form of the word practice.
In British English, practice is used as a noun and practise is used as the verb form of practice. According to the Cambridge Advanced Learner's Dictionary, the word practise as a verb refers to training, activity and work. For example, "I am going to practise the piano every day" uses the verb form; whereas, "It is not our practice to accept checks as a form of payment" uses the same word but in noun form.
The distinction between the words practise and practice is observed in the United Kingdom, which includes England, Scotland, Wales, and Northern Ireland. This distinction is also observed in the British English speaking countries including Australia, New Zealand, South Africa and Canada. In each of these countries, it is correct to use practise as the verb form of the noun practice.
The distinction between the words practise and practice is not observed in the United States and the former is not commonly used in American English. In addition to not being recognized in U.S. spell check programs, most American English dictionaries and reference guides specify that practise is the British or UK version of the word practice.