Select the most appropriate one-word substitution for the given words.

a seven-sided figure

heptagon

The most appropriate one-word substitution for the given words is heptagon.

• Hexagon is a six-sided figure.
• Pentagon is a five-sided figure.
• Octagon is an eight-sided figure.

A heptagon is a seven-sided figure. It is a polygon with seven sides and seven angles. Heptagon is the most appropriate one-word substitution because it is the only word that specifically refers to a seven-sided figure.