from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A geometric curve traced by a fixed point on the radius line outside one circle which rotates inside the perimeter of another circle.
from the GNU version of the Collaborative International Dictionary of English
- n. A curve, traced by a point in the radius, or radius produced, of a circle which rolls upon the concave side of a fixed circle. See hypocycloid, epicycloid, and trochoid.
from The Century Dictionary and Cyclopedia
- n. A curve which can be traced by a point rigidly connected with a circle which rolls upon the interior of another circle.
hypo- + trochoid (Wiktionary)
I saw a hypotrochoid drawing kit for sale around Christmas this year, and not the canonical Spirograph, either.