Turns out it often depends on context: <a href="https://www.nasdaq.com/articles/indexes-or-indices-whats-the-deal-2016-05-12" rel="nofollow">https://www.nasdaq.com/articles/indexes-or-indices-whats-the...</a><p>[..]
"Indices" is originally a Latin plural, while "Indexes" has taken the English way of making plurals, using –s or –es.<p>"Indices" is used when referring to mathematical, scientific and statistical contexts. It is used to refer to a numbers, symbols, and figures comparing a value to a standard.<p>"Indexes" is usually used in reference to written documents, such as bibliographical or citation listings.
[..]<p>Based on that definition “indexes” is probably more common in the context of databases than indices which makes me suspect it’ll win in this poll given the audience of HN.