What do you call a shape with 7 or 9 points?

It's always a triangle for 3 sides / apices; but the root "trigon" is of course half of the word trigonometry; the mathematics of ttiangles and angles.

5 points = pentagon. ("hect[o]" is the prefix for 100 in SI units, e.g. 1 hectometre = 100 metres).

7 points = septagon

9 points = nonagon.

11 points = ? I'm not sure it has a name!

12 points = dodecagon.

(A 12-facet solid is a dodecahedronm, and each facet of a regular dodecahedron is a regular pentagon in outline. I once made a pomander to that shape, approximately three inches across, as a Christmas present to a girlfriend. This is a common shape for military radar and radio aerial enclosures.)