The Collaborative International Dictionary of English v.0.48:

Cycloid \Cy"cloid\ (s?"kloid), n. [Cyclo- + -oid: cf. F.
   cyclo["i]de.] (Geom.)
   A curve generated by a point in the plane of a circle when
   the circle is rolled along a straight line, keeping always in
   the same plane.
   [1913 Webster]

   Note: The common cycloid is the curve described when the
         generating point (p) is on the circumference of the
         generating circle; the curtate cycloid, when that point
         lies without the circumference; the prolate or
         inflected cycloid, when the generating point (p) lies
         within that circumference.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Cycloid \Cy"cloid\, a. (Zool.)
   Of or pertaining to the Cycloidei.
   [1913 Webster]

   Cycloid scale (Zool.), a fish scale which is thin and shows
      concentric lines of growth, without serrations on the
      margin.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Cycloid \Cy"cloid\, n. (Zool.)
   One of the Cycloidei.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Brachystochrone \Bra*chys"to*chrone\, n. [Incorrect for
   brachistochrone, fr. Gr. bra`chistos shortest (superl. of
   brachy`s short) + ? time : cf. F. brachistochrone. ] (Math.)
   A curve, in which a body, starting from a given point, and
   descending solely by the force of gravity, will reach another
   given point in a shorter time than it could by any other
   path. This curve of quickest descent, as it is sometimes
   called, is, in a vacuum, the same as the cycloid.
   [1913 Webster]

WordNet (r) 3.0 (2006):

cycloid
    adj 1: resembling a circle [syn: cycloid, cycloidal]
    n 1: a line generated by a point on a circle rolling along a
         straight line