Geometric Nomenclature 101

Can't tell a triacontakaiheptagon from a hectohexacontatrigon? Fear no more. Soon you'll be able to include Greek numerology and geometric nomenclature on your curriculum vitae.

Polygonal prefixes are of greek origin. So if you think a heptagon should really be called a septagon, sorry but sept- comes from the Latin septum, whereas the Greek prefix for seven is hepta. Another tricky one to look out for is enneagon, a nine-sided polygon. Nonagon is also commonly accepted these days, but it helps to be able to recognise the alternatives.

Units

1 hena-
2 di-
3 tri-
4 tetra
5 penta-
6 hexa-
7 hepta-
8 octa-
9 ennea-

10 decagon
11 hendecagon, undecagon
12 dodecagon

Teens

13 triskaidecagon
14 tetrakaidecagon
15 pentakaidecagon
16 hexakaidecagon
17 heptakaidecagon
18 octakaidecagon
19 enneakaidecagon

Tens

10 decagon

20 icosagon
icosikai + unit prefix

30 tricontagon
tricontakai + unit prefix

40 tetracontagon
tetracontakai + unit prefix

50 pentacontagon
pentacontakai + unit prefix

60 hexacontagon
hexacontakai + unit prefix

70 heptacontagon
heptacontakai + unit prefix

80 octacontagon
octacontakai + unit prefix

90 enneacontagon
enneacontakai + unit prefix

100 hectogon
hecta + tens prefix + unit prefix

1000 chiliagon

10000 myriagon