Greek number prefixes
Pentagon, hexagon, decathlon, kilometre: English counts in Greek more often than it seems. Each prefix below sits beside the Ancient Greek it came from and the Modern Greek number a learner meets today.
| Prefix | Value | Ancient Greek | Modern Greek number | English words |
|---|---|---|---|---|
| mono- | 1 | μόνος, alone | ένα (μόνος still means alone) | monologue, monotone, monopoly |
| di- | 2 | δίς, twice | δύο | dilemma, dioxide, diphthong |
| tri- | 3 | τρι-, from τρεῖς | τρία | tripod, trilogy, trigonometry |
| tetra- | 4 | τετρα-, from τέτταρες | τέσσερα | tetrahedron, tetrapod |
| penta- | 5 | πεντα-, from πέντε | πέντε | pentagon, pentathlon |
| hexa- | 6 | ἑξα-, from ἕξ | έξι | hexagon, hexameter |
| hepta- | 7 | ἑπτα-, from ἑπτά | εφτά | heptagon, heptathlon |
| octa-, octo- | 8 | ὀκτα-, ὀκτω-, from ὀκτώ | οχτώ | octagon, octopus |
| ennea- | 9 | ἐννεα-, from ἐννέα | εννιά | ennead, enneagon |
| deca- | 10 | δεκα-, from δέκα | δέκα | decade, decathlon, decagon |
| hendeca- | 11 | ἑνδεκα-, from ἕνδεκα | έντεκα | hendecagon, hendecasyllable |
| dodeca- | 12 | δωδεκα-, from δώδεκα | δώδεκα | dodecahedron, dodecagon |
| icosa- | 20 | εἰκοσα-, from εἴκοσι | είκοσι | icosahedron |
| hecto- | 100 | from ἑκατόν | εκατό | hectare, hectolitre, hectopascal |
| kilo- | 1,000 | from χίλιοι | χίλια | kilogram, kilometre, kilowatt |
| myria- | 10,000 | μυριάς, ten thousand | δέκα χιλιάδες | myriad, myriapod |
Prefixes as a way into the numbers
Most of these prefixes still look like the Modern Greek word: penta- and πέντε, deca- and δέκα, dodeca- and δώδεκα. A few have drifted. Ten thousand, μυριάς, is no longer a number word in Modern Greek; μύρια now means countless, the same sense as English myriad. Modern Greek says δέκα χιλιάδες.
The Triantafyllidis dictionary lists the combining forms too, with their international spellings: its entry for επτά- / εφτά- gives the international hepta-, and Modern Greek builds new words with them, εξάγωνο (hexagon), πεντάγωνο (pentagon), δεκάλεπτο (ten minutes).
Questions teachers and learners ask
What are the Greek prefixes for numbers?
mono- (1), di- (2), tri- (3), tetra- (4), penta- (5), hexa- (6), hepta- (7), octa- (8), ennea- (9), deca- (10), hendeca- (11), dodeca- (12), icosa- (20), hecto- (100), kilo- (1,000) and myria- (10,000). They come from Ancient Greek and are the ones used in geometry, chemistry and the metric system.
Is mono- the Greek for one?
Not exactly. mono- comes from μόνος, alone or only, which is still an everyday Modern Greek word. The number one is ένα. English took the "alone" word for its prefix, which is why monologue means one person speaking alone.
Where do kilo- and hecto- come from?
From Greek, by way of France. The designers of the metric system in the 1790s took the Greek words for a thousand and a hundred, χίλιοι and ἑκατόν, for the multiplying prefixes, and Latin for the dividing ones (milli-, centi-). So a kilometre is a thousand metres and a hectare a hundred ares.
Do Greek number prefixes help with learning Modern Greek numbers?
Yes, more than most languages’ prefixes, because Modern Greek kept the same words. Pentagon gives πέντε, decade gives δέκα, dodecahedron gives δώδεκα. Four and a thousand are the ones that have moved furthest: tetra- beside τέσσερα, kilo- beside χίλια.
Sources: Λεξικό της κοινής νεοελληνικής (Triantafyllidis Foundation), combining-form entries such as επτά- (“διεθ. hepta-”); Wiktionary etymologies of the English words listed; the International Bureau of Weights and Measures (BIPM), SI Brochure, on the origin of the SI prefixes.