-ces

Used to form the irregular plural form of Latin-derived nouns ending in x:

Suffix

  1. Used to form the irregular plural form of Latin-derived nouns ending in x:
    • ⟨-ax⟩ thorax → thoraces
    • ⟨-ex⟩ scolex → scoleces, index → indices
    • ⟨-ix⟩ helix → helices

Origin

Derived from the pluralization pattern of Latin third declension nouns.