I was having a fairly typical conversation with a very good English friend tonight, when he asked what seemed a simple question. Why is the United States 10 cent piece, called a dime? Well, we’ve pretty much deduced all coins except that one. I’ve researched all over the web, and am unable to come up with a reasonable answer. Can you helpl? (I know that you can—I’ve just spent the last hour reading through the postings…I laughed and laughed.) Thank you.
Jefferson coined the term disme, from the French dixieme, for a tenth of a dollar. Pronounced deem, it eventually became dime.
See how easy that was? Welcome to the SDMB! 
According to Dictionary.com:
[quote]
Middle English, tenth part, from Old French disme, from Latin decima (pars), tenth (part), from decem, ten. See dek in Appendix I.* acknowledgement
WOW! A 3-way simul-post, with roughly the same information in each. Two from exactly the same source. I wish I could get that kind of response from my cable company!