In US English, only licence and practice are used for either the verb or the noun. But in British and Australian English, the verb takes ‘s’ and the noun takes ‘c’. How do you remember? Here’s a simple and filthy saying to help you. Being a Cock doesn’t require a liCence but takes some practiCe. Once you’ve practiSed Stupidity a lot, though, you may become licenSed.
So, Lily, next time you're stumped, remember: If it's a noun, licence and practice take C (C for cock), if it's a verb, license and practise take S (S for stupid).