Mike Stone asks about the difference between practice and practise, defence and defense.
Are they UK/US differences or is it something to with their use as nouns/verbs. I’ve never been able to find a good simple explanation.
Differences between some -ce, -se words do reflect a difference between British and American spelling.
British: defence, offence, pretence,
American: defense, offense, pretense
As for practice, practise, making a distinction in spelling between the noun and the verb is British usage:
practise [prăk’tĭs] (verb) – The doctor plans to practise medicine in Yorkshire.
practice [prăk’tĭs] (noun) – He hopes to build up quite a good practice.
In American usage, both the noun and verb forms are spelled the same:
The doctor practiced medicine in his home town.
In the case of advise and advice, however, both British and American usage agree:
advise [ ăd-vīz’ ] verb – He advised the students to take typing.
advice [ ăd-vīs’ ] noun She was glad that she followed his advice.
NOTE: I must have lived in the UK too long: pretence looks better to me than pretense!