Helix

In academic English, the plural of helix should always be helices.

helix is a word used in mathematical descriptions, or descriptions echoing mathematics. It means “a coil, a spiral, [such] as an electromagnetic coil of wire, the thread of a screw, a tendril … [more accurately] Anything of a spiral or coiled form, whether in one plane (like a watch-spring), or advancing around an axis (like a corkscrew), but more usually applied to the latter” (OED). Its most famous use in modern English is in the phrase ‘the double helix’ to describe the molecular structure of DNA.

helix was originally a Greek word which was taken first by Latin, where the normal plural of words ending in -ix is –ices (see also index, appendix). In academic English, use the Latin or Greek forms of words that still ‘feel’ as if they are Latin or Greek, as far as you can.