Liquorice is pronounced ˈlɪkərɪʃ. But every other word I can think of ending with -ice is pronounced differently (such as police or rice). How did liquorice get such a strange pronunciation, or alternatively, to be spelt like that?
It actually used to be pronounced /lɪkoɹˈɛs/, as evidenced by the Old French word we borrowed it from, "licoresse".
The last phoneme probably shifted from /s/ to /ʃ/ due to a similar process that happened with the words "pressure" and "sugar".
Why it changed and not other similar words? Who knows. English speakers for a long time have had a twisted lack of consistency. Why are the two words, from the same language and borrowed at roughly the same time period, "prestige" and "vestige" pronounced so differently?
As a supplement: The pronunciation with [ɪʃ] may also have been influenced by a very old variant of what is now lecherous: lickerish, which broadened its sense to "greedy, desirous" and at one time had the side meaning "tempting to the appetite".
I had this argument in school with my English teacher; I pronounced it with the iss, not the ish. She showed me a dictionary where it was pronounced ish, but instead of taking her word I decided to do some research in older dictionaries... we were both right. The original way was the way I had said it with the iss sound, but due to an overwhelming amount of people pronouncing it ish it was changed. Shortly after it had been changed, there were two ways printed and an explanation, but now it seems this has been lost over the years and simply changed to ish. I refuse to roll with the masses and still pronounce it iss not ish.
Ah well, it is my choice; and in my mind, I am equally correct saying it this way.
It's possible that the pronunciation of the common noun liquorice was influenced by the plant's Latinized genus name Liquiritia, anglicized as /lɪkwɪɹɪʃə/ (and these days less often used than the official Greek name Glycyrrhiza). Other plants where English speakers tend to use the genus name more than the English name include eucalyptus (gum tree) and ficus (weeping fig).
So if people sometimes heard the term Liquiritia in reference to liquorice, the pronunciations might have converged over time. This convergence may have been helped along by the fact that the English word can be traced back to the Latin one through French.
Liquorice (American English: licorice) is a word that derives from the Old French licoresse (the equivalent of the modern French règlisse). The English word kept the pronunciation of the original word.
There is another word that has a similar pronunciation of -rice, and that has origin from a French word: caprice (AmE /kəˈpris/, BrE /kəˈpriːs/).