Definition of cissoid
: a plane curve with two branches meeting at a cusp at one end of a diameter of a fixed circle, each point of the cissoid being obtained by going from the cusp along any chord to its intersection when extended with the tangent diametrically opposite the cusp and then returning along the extended chord a distance equal to the length of the chord
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Origin and Etymology of cissoid
Late Greek kissoeidēs, from Greek, like ivy, from kissos ivy + -oeidēs -oid
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