A line generated by a point on a circle rolling around another circle.

Roget 247: circularity, roundness; rotundity etc. 249.    circle, circlet, ring, areola, hoop, roundlet^†, annulus, annulet^†, bracelet, armlet; ringlet; eye, loop, wheel; cycle, orb, orbit, rundle, zone, belt, cordon, band; contrate wheel^†, crown wheel; hub; nave; sash, girdle, cestus^†, cincture, baldric, fillet, fascia, wreath, garland; crown, corona, coronet, chaplet, snood, necklace, collar; noose, lasso, lassoo^†.    ellipse, oval, ovule; ellipsoid, cycloid; epicycloid [Geom.], epicycle; semicircle; quadrant, sextant, sector.    sphere etc. 249.    ... show more

Dutch: epicycloïde, cycloïde
Polish: epicykloida