An elderly acquaintance of mine who recently celebrated his 100th birthday used the phrase "lexicographical heteromorphs" for these linguistic abominations that use mixed roots. Undecagon and duodecagon are such in that they unite Latin prefixes with Greek suffices. A subsequent reply correctly gives hendecagon for 11 sides and dodecagon for 12. Also the Susan B. Anthony $1 coin for the U.S. was in the shape of a regular hendecagon. These still exist, but are rarely seen in circulation. Since the 13-gon, 14-gon, 18-gon, 19-gon are not constructable with compass and straight edge, other than for linguistic curiosity, why would one want to name them? However, what name does one give to the 24-gon, the 48-gon, and the 96-gon; those polygons which were useful in the early approximations of PI?