Plural of “codex”

The plural of codex is codices.

Why

"Codex" is Latin for a block of wood, and by extension a set of wooden writing tablets bound together — the ancestor of the modern bound book, as opposed to a scroll. Because the word is almost exclusively used today in scholarly, historical, and bibliographic contexts (ancient manuscripts, medical or pharmaceutical reference codices, legal codices), it has never developed a naturalized English plural the way more everyday Latin borrowings sometimes do.

"Codices" (koh-dih-seez) is essentially the only plural you'll encounter in reputable usage; unlike "apex" or "vortex," "codexes" barely registers as an alternative in dictionaries or in practice, because the word simply hasn't drifted into casual, high-frequency everyday speech the way those other words have.

Usage note

Use "codices" in any context — historical, academic, or bibliographic — since it's the expected and essentially unchallenged form. There's no register where "codexes" is the safer or more natural choice.

The word is closely related to "code" (as in legal code, source code), both descending from the same Latin root, but "code" long ago became a fully naturalized English word with its own regular plural, "codes," while "codex" stayed specialized enough to keep its Latin form intact. Beyond ancient manuscripts, "codex" survives today in pharmaceutical and food science terminology — the "Codex Alimentarius," an international collection of food standards maintained jointly by the UN's Food and Agriculture Organization and World Health Organization, uses the word in its original singular sense, while researchers discussing multiple such regulatory codices still default to the Latin plural without exception.

Common real mistakes

Writers sometimes confuse "codex" with "index," assuming the plural should follow the same familiar -exes/-ices pattern debate — but "codices" carries almost none of the competition "indices/indexes" does; stick with "codices" without hesitation.

The wider pattern

"Codex" is the clearest case among the Latin -ex nouns here of a word that stayed a specialist term long enough to never develop a rival English plural, standing in contrast to "complex" and "annex," both of which fully anglicized and shed their Latin plural potential entirely. The shift from scroll to codex in the early centuries CE is considered one of the most significant developments in the history of the book, since codices allowed random access to any page rather than forcing readers to unroll an entire scroll sequentially, a practical advantage that helped the format spread rapidly through both religious and secular writing.

Examples

• The library holds three medieval codices copied by the same scribe.
• Scholars have studied the surviving codices of the ancient text for centuries.
• Several codices were damaged in the fire that swept through the abbey.
• The exhibit displayed illuminated codices dating back to the ninth century.
• Researchers compared variant readings across a dozen surviving codices.
• Two codices in the collection contain entirely different endings to the same story.
• The pharmacopeia includes several regional codices listing approved remedies.
• Conservators are digitizing the fragile codices before they deteriorate further.
• The museum's codices represent some of the oldest bound texts in existence.
• Historians traced the manuscript's lineage through four surviving codices.
• The rare book room keeps its most fragile codices under climate control.
• Two codices from the same monastery ended up in different countries.
• Digitization projects have made previously inaccessible codices available online.
• The forger's fake codex was eventually exposed through ink analysis.
• Historians credit the codex format with making random-access reading possible for the first time.
• Several early Christian codices survive only in fragments today.
• The library's rarest codices are kept in a separate, climate-controlled vault.
• Scholars compared handwriting styles across a dozen medieval codices.
• The exhibit's most fragile codices are displayed under low lighting.
• Two codices offer conflicting accounts of the same battle.