epitrochoidn.
/ɛpɪˈtrɒkɔɪd/ Mathematics.
The curve described by a point rigidly connected with the centre of a circle which rolls on the outside of another circle. Cf. epicycloid n.
ΚΠ
1843 Penny Cycl. XXV. 284/2.
1879 W. Thomson & P. G. Tait Treat. Nat. Philos. (new ed.) I: Pt. i. §94.
Derivatives
epitroˈchoidal adj. of or pertaining to an epitrochoid.
ΘΚΠ
the world > movement > motion in a certain direction > movement in circle or curve > [adjective] > curved (of movement) > specific type of curve
epitrochoidal1800
1800 Philos. Trans. (Royal Soc.) 90 149 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.
1959 Times 15 Dec. 7/1 The shape of the bore in which the triangular rotor revolves is described as epitrochoidal: the shield-shaped piston moves round the inside of a cavity like the hollow skin of an Edam cheese.
1969 Observer 23 Mar. (Colour Suppl.) 27/1 Take the revolutionary Wankel engine. Twin rotors in an epitrochoidal bore. That's two rotors going round and round, instead of four or more pistons going up and down.
This entry has not yet been fully updated (first published 1891; most recently modified version published online March 2021).
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n.1800