View source for Prefixes in words for geometrical figures

The prefixes in English words for two- and three-dimensional geometrical figures generally derive from the Greek words for the numbers. See [[Greek and Latin words for numbers]]. There are some exceptions - in the case of the words for two-dimensional figures with three, four, or nine sides, as noted in the first table below.

As you will see, the words for two-dimensional (i.e., plane) figures are usually formed by adding the prefix to the stem -gon.  This stem comes from the Greek word ''gonia'', which means 'corner or angle'. The words for three-dimensional (i.e., solid) figures are formed by adding the prefix to the stem -hedron. This stem comes from the Greek word ''hedra'', which means 'seat or base'.


{| border="1" cellpadding="2"
|+ '''Words for plane (i.e., two-dimensional) geometrical figures'''
|-
! No. of sides !! Name of figure !! Comments
|-
| 3 || triangle || This derives from the Latin ''tres'' (three) and ''angulus'', meaning 'corner or angle'. The Greek-derived 'trigon' is archaic.
|-
| 4 || quadrilateral || This derives from the Latin ''quattuor'' (four) and ''latus''/''lateris'', meaning 'side'. The Greek-derived 'tetragon' is archaic.
|-
| 5 || pentagon || -
|-
| 6 || hexagon || -
|-
| 7 || heptagon || -
|-
| 8 || octagon || -
|-
| 9 || nonagon || 'nona-' comes from the Latin ''nonus'', meaning 'ninth'. The Greek-derived 'enneagon' is also possible.
|-
| 10 || decagon || -
|-
| 11 || hendecagon || -
|-
| 12 || dodecagon || -
|}


{| border="1" cellpadding="2"
|+ '''Words for solid (i.e., three-dimensional) geometrical figures'''
|-
! No. of faces !! Name of figure !! Comments
|-
| 4 || tetrahedron || A pyramid is one type of tetrahedron. A regular tetrahedron has four plane sides which are equilateral triangles.
|-
| 5 || pentahedron || -
|-
| 6 || hexahedron || A regular hexahedron is a cube.
|-
| 7 || heptahedron || -
|-
| 8 || octahedron || -
|-
| 9 || enneahedron || -
|-
| 10 || decahedron || -
|-
| 11 || hendecahedron || -
|-
| 12 || dodecahedron || -
|-
| 20 || icosahedron || -
|}


See also [[Greek and Latin words for numbers]], [[Prefixes in units of measurement]], [[Prefixes for very high numbers]], and [[Greek or Latin numerical prefix?]].

[[Category:Prefixes]][[Category:Numbers]][[Category:Greek]][[Category:Latin]][[Category:Etymology]]