‘This is not easy for me to contemplate and has troubled me for many years - I recall my reluctance to accept the theory that some trigons on a diamond octahedron were produced by dissolution.’
‘It is therefore not enough to count trigons by signs or to expect a true square from signs at intervals at four’.’
‘You can also have a cylinder cone roof wedge trigon prism.’
Origin
Early 17th century (in the sense ‘triangle’): via Latin from Greek trigōnon, neuter of trigōnos ‘three-cornered’.
Are You Learning English? Here Are Our Top English Tips