| Semicircle 1. (n.) The half of a circle; the part of a circle bounded by its diameter and half of its circumference. 2. (n.) A semicircumference. 3. (n.) A body in the form of half of a circle, or half of a circumference. 4. (n.) An instrument for measuring angles. Thesaurus Entries crescent, crescent moon, fifty percent, fifty-fifty, half, half circle, half-and-half, half-moon, hemicycle, hemisphere, horseshoe, lunula, lunule, mediety, meniscus, moiety, quadrant, scythe, sector, semisphere, sextant, sickle |