Math. [f. Gr. ἐπί upon + τροχός wheel + -OID; after analogy of epicycloid.] The curve described by a point rigidly connected with the center of a circle that rolls on the outside of another circle. Cf. EPICYCLOID.
1843. Penny Cycl., XXV. 284/2.
1879. Thomson & Tait, Nat. Phil., I. I. § 94.
Hence Epitrochoidal a., of or pertaining to an epitrochoid.
1800. Phil. Trans., XC. 149. Epitrochoidal curves, formed by combining a simple rotation or vibration with other subordinate rotations or vibrations.
1843. Penny Cycl., XXV. 284/2. Every direct-epicycle planetary system is both epitrochoidal and externally hypotrochoidal.
