In Oxford Learner's Dictionary, under Achilles tendon, it says that

  • Achilles tendon = Achilles

Then the plural of 'Achilles tendon' is 'Achilles tendons'.

But, what is the plural form of "Achilles"?


Why should you want "the plural of Achilles"? Nouns (common or proper) used as the non-final element of compounds don't usually take a plural ending; and if they do, they always take it. They don't change when the whole phrase is plural:

kitchen unit -> kitchen units.

cable provider -> cable providers.


glasses case -> glasses cases.

If you really want to talk about more than one Achilles, then most people would say "Achilleses", but people often aren't sure how to write it. I suspect some people would say "two Achilles" (like "two series").


Google finds around a dozen hits for "two achilles are", and only one for "two achilleses are". So I would say the consensus is that the plural of Achilles is Achilles.

However pluralizing achilles is so rare that I assume most people who do it aren't copying the plural form from things they've heard, but coming up with it de novo. So I would be very heistant to call achilleses wrong.

  • 2
    Perhaps it's because words ending in unstressed /iz/ already "sound" plural: fillies, axis>axes, basis>bases, crisis>crises, Kingdom of the Two Sicilies, gives me the willies. – tchrist Dec 15 '18 at 19:03
  • @tchrist: that's probably why. And two additional words: species>species and series>series. – Peter Shor Dec 16 '18 at 16:21
  • Be­sides those two you note from Latin’s 5ᵗʰ-de­clen­sion, other ex­am­ples in­vari­ant in the plu­ral be­cause of al­ready end­ing in un­stressed /iːz/ (UK) or /iz/ (US) are Pekinese for the dog and Si­amese for the cat. As far as I can dis­cern, ᴀʟʟ -ese de­monyms and lo­gonyms end­ing in un­stressed /iz/ strongly re­sist (block?) fur­ther /ǝz/ in­flec­tions, whether to make them plu­ral or to make them pos­ses­sive. Same with Mercedes be­ing in­vari­ant, be it car make or wom­an’s name. That’s why I be­lieve these all op­er­ate un­der some kind of un­taught sound law. – tchrist Dec 16 '18 at 17:34

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