Link to the appropriate column follows: http://www.straightdope.com/classics/a3_252.html
I’m afraid I must correct. The suffix -gon denotes two-dimensional shapes, as in ‘pentagon’ or ‘octagon.’ When referring to three dimensional solids, the suffix appropriate to the situation becomes -hedron (sometimes seen pluralized as -hedra, though -hedrons is preferred). So we have nonhedrons (nine-sided solids), dodekahedrons (twenty-sided solids), and thus, triskaidekahedrons (thirteen-sided solids).
–Adam, linguistics student and die collector