Ten
ten (Old English *tīen*) — the cardinal numeral following nine, ancestor of an entire numerical vocabulary spanning every branch of Indo-European.
The PIE Root
Proto-Indo-European *\*déḱm̥* is one of the best-attested roots in the language family, reconstructed with confidence from cognates across every branch. The root appears with striking regularity: Sanskrit dáśa, Greek déka, Latin decem, Gothic taihun, Old English tīen, Lithuanian dešimt, Russian desyat', Welsh deg, Armenian tasn. When a root survives intact from Ireland to India, it signals something fundamental — a concept so embedded in daily life that no migration or conquest could dislodge it.
The numeral ten was that foundational. It organised markets, divided land, structured armies, measured harvests. Where the word travelled, the decimal system travelled with it.
Grimm's Law and the Germanic Shift
English *ten* looks nothing like Latin *decem* or Greek *déka*, yet all three descend from the same PIE root. The divergence is systematic, not random. Grimm's Law describes a regular consonant shift that separated Germanic languages from the rest of Indo-European: PIE *\*d* shifted to Germanic *\*t*, PIE *\*k* shifted to Germanic *\*h*.
The result: PIE *\*déḱm̥* → Proto-Germanic *\*tehun* → Old English *tīen* → Modern English *ten*. Latin conserved the original stops (*decem*), Greek conserved them (*déka*), but every Germanic language shifted them by the same rules.
English Gets Two Forms
Because English absorbed Latin and Greek wholesale through the Norman Conquest and Renaissance scholarship, it now carries two distinct lineages of *\*déḱm̥*:
Germanic: ten, tithe (a tenth part), teen (as in thirteen, fourteen), -ty (as in twenty, thirty)
Greek and Latin: decade, decimal, decimate, December, dean, dime, dozen, decathlon, decibel, decagon
The two strands serve different registers. *Ten* is the everyday numeral; *decimal* is the technical term.
December Was the Tenth Month
Latin *decem* is preserved in the name December, but modern December is the twelfth month. The discrepancy is a fossil of Roman calendar history. The original Roman calendar began in March and ran ten months — *Martius* through *December*. January and February were added later, pushing every month two positions forward. September (septem, seven), October (octo, eight), November (novem, nine), and December (decem, ten) all carry their original numerical names while occupying positions two months later.
Decimate
The Latin verb decimare meant precisely *to select every tenth one*. Roman military commanders used decimation as collective punishment: a unit was divided into groups of ten, lots were drawn, and the unlucky one-in-ten was beaten to death by his comrades. The survivors were shamed and diminished.
Decimate entered English in the 1600s carrying this exact meaning. Its modern use to mean *destroy a large part of* is a semantic broadening that has been happening for four hundred years. The original meaning survives in the etymology: every use of *decimate* contains the ghost of the number ten.
Dean: Leader of Ten
The Latin word decanus — from *decem* — meant an officer in charge of ten men. In the early Church, a *decanus* supervised ten monks. The word passed through Old French as doyen (still the French word for the senior member of a group) and into Middle English as dean. Today a university dean administers a faculty; a cathedral dean oversees a chapter. The original unit of ten men persists in the title's etymology.
Dozen: Two Plus Ten
Ten and the Right Hand
One proposed etymological connection links PIE *\*déḱm̥* to PIE *\*deḱs-*, meaning *right* or *right hand* (source of Latin *dexter*, English *dexterous*). The hypothesis is that *ten* was conceptualised as *the complete count* — the point at which you have used both hands and arrived back at the right, your starting hand. The decimal system would then be not merely a counting convenience but a bodily fact: ten fingers, ten as completion, the right hand as the anchor of the full count.
The Cognate Chain
Few roots demonstrate the unity of Indo-European more plainly than *\*déḱm̥*. A speaker of Sanskrit *dáśa* and a speaker of Welsh *deg* inherited the same word across four thousand years of separation. The word for ten, in one form or another, is the same word from the Atlantic coast of Wales to the plains of northern India.