In the shape of half of a circle or a semicircle. (adjective)
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Use "semicircular" in a sentence
"Attached to the utricle are three tubes that start and end there, each bending in a semicircle so they are called semicircular canals."
"The principal charm, however, belongs to the grotto with the river which it discharges -- the site of which may be described as a semicircular termination of a valley on a natural platform half way up a cliff -- the water tumbles down in short cascades for some distance; the grotto inside is untouched by chisel squarings or embellishment, just as Juvenal wished the grot of AEgeria to be."
"At the far end was a kind of semicircular nave with built-in benches, which reminded me of a sauna."