The Collaborative International Dictionary
Heptagonal \Hep*tag"o*nal\, a. [Cf. F. heptagonal.] Having seven angles or sides.
Heptagonal numbers (Arith.), the numbers of the series 1, 7, 18, 34, 55, etc., being figurate numbers formed by adding successively the terms of the arithmetical series 1, 6, 11, 16, 21, etc.
Wiktionary
a. 1 Having seven angles and sides. 2 (context math of a number English) Belonging to the sequence generated by the formula .
Usage examples of "heptagonal".
Beginning from the bottom on the left-hand side, there was a dot - it was too neatly circular to be accidental - a flat-topped equilateral triangle, a pentagon and then a heptagonal figure.
The control room was arranged in a heptagonal shape, with seven acceleration couches facing one to each side.
She was crouched on the floor in front of him, holding up a heptagonal glass bottle that appeared to be empty.
Aine followed me back to the hatch, where Manaan was brandishing my little heptagonal glass bottle.
For a building that looks like simplicity itself on the outside--seven triangular blocks arranged in a star shape around a heptagonal inner courtyard--the Pharc is a very confusing place once you get indoors.
As we came closer, we realized that the quadrangular form included, at each of its corners, a heptagonal tower, five sides of which were visible on the outside—four of the eight sides, then, of the greater octagon producing four minor heptagons, which from the outside appeared as pentagons.