The Correct Plural for "Sustainability Index"

I took Latin for two years when I was growing up, and as a result have a freakishly strong reaction when I hear corrupted versions of words taken directly from ancient languages. This aversion kicked in the other day when I was told that the "correct" plural for sustainability index is sustainability indexes. If this is truly the case, then I have some egg on my face based on my post about the Dow Jones Sustainability Index.

Or do I? A bit of quick research gave me reason to question what I had been told. Yahoo! Finance, FTSE, MSCI Barra, Nasdaq, NYSE, Reuters and S&P use indices as the plural, leaving me with some confidence that I may be in the right. On the other hand, Bloomberg, Dow Jones, Russell adopt the more modern indexes convention, indicating that there is no consensus in this area.

With no clear answer to this question, I am sticking to my guns and continuing to use indices when I refer to a sustainability index and its brethren. I hope that this does not make YOU bristle.

Photo credit: Katrina Tuliao