How many letters does the top answer for “a plane figure with the shape of half a circle” have?

The most common answer is hemicycle (9 letters).

Crossword clue: a plane figure with the shape of half a circle

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

hemicycle 9 letters wn-def

a plane figure with the shape of half a circle

semicircle 10 letters wn-def

a plane figure with the shape of half a circle