When ever this happens to me, I just use the correct form over and over again in multiple sentences. The caller should not correct the client. He should use "index" as much as possible and passively educate him/her on the correct term. "I noticed that the DOW index was trading higher today, while the S&P index and the Nasdaq index were both lower. It is a good thing that your index fund follows the DOW index."

The discussion on index and indece was interesting. It surprised me when the indice term was indicated as not being real, (my unabridged dictionary agreed on it not being real, durn it) I have commonly used index as a fixed number or the result of a study, and indice as the immeadiate or approximate value, which when recorded would become an index. Index had more impact than indice. I will probably continue using the two terms, but, hopefully will only use "index" in reports or presentations.

I work for one of those companies that calculate financial indices. They should have guessed what kind of employee they were getting when, during my interview, I asked if the company standard plural was “indexes” or “indices.” Our documentation is consistent in using “index” / “indices.” However, in less formal contexts, you will hear “indexes” and you do hear *”indice” from time to time.

By the way, in college, my roomates and I used the plural “kleenices” as well.

To avoid the awkwardness at Starbucks — I can't stand the looks I get when I buy a biscotto — I usually turn the phrase to “one of your biscotti” or “one of the panini.” My wife is used to my asking for a taste of a raviolo from the meal she has ordered.

It took me a while. After my "biscotto" phase, I started ordering two biscotti, even when I only wanted one. Then I would order two biscotti, and quickly add "Make that one!" That led me naturally to this most recent, and satisfactory end.

I have been noticing an interesting pronunciation of “indices” from some of my colleagues who are not native English speakers — as if something were imbedded into finely cubed vegetables: in dices (rhymes with ices). Everyone seems to know what they are talking about, but as the new guy, it took me a while to put it together.