How many letters does the top answer for “a plane figure consisting of seven sides and having seven angles.” have?

The most common answer is heptagon (8 letters).

Crossword clue: a plane figure consisting of seven sides and having seven angles.

1 answer found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

heptagon 8 letters web-def

a seven-sided polygon

a figure having eleven angles and eleven sides. 50% similar → undecagon

a plane figure of eleven sides and angles. 50% similar → endecagon

a plane figure of eleven sides and eleven angles. 50% similar → hendecagon