Definitions
from Wiktionary, Creative Commons Attribution/ShareAlike License
 n. Any of a family of curves defined as the locus of a point, P, on a line from a given fixed point to a given curve, C, where the distance along the line from C to P remains constant.
from the GNU version of the Collaborative International Dictionary of English
 n. A curve, of the fourth degree, first made use of by the Greek geometer, Nicomedes, who invented it for the purpose of trisecting an angle and duplicating the cube.
from The Century Dictionary and Cyclopedia
 n. A plane curve invented by one Nicomedes, probably in the second century before Christ, and defined by him as such that if a straight line be drawn from a certain fixed point, called the pole of the curve, to the curve, the part of the line intercepted between the curve and a fixed line (now called its asymptote) is always equal to a fixed distance.
 n. It is a curve of the fourth order and of the sixth class, unless it has a cusp at P, when it is of the fifth class. It has a double point at the pole, and meets its asymptote at four consecutive points at infinity. It has two branches.
 Same as conchoidal.
Etymologies
from Wiktionary, Creative Commons Attribution/ShareAlike License
Examples

Apollonius, was the inventor of the _conchoid_ or _cochloid_, of which, according to Pappus, there were three varieties.

The areas of visibility for 23 of these eclipses were conchoid and for 12 were cylindrical.

The curves for the areas in which an umbral eclipse is viewed as partial are of two sorts: cylindrical and conchoid.

For conchoid eclipses, outside the polar regions, that area extended from 1 to 2⅝ inches at right angles to the path of the umbral eclipse and from ⅜ to 1 inch from the ends in the direction of that path.

The = pileus = varies from a regular wedgeshape to spathulate, or more or less irregularly petaloid, or conchoid forms, the extremes of size and form being shown in Figs. 112, 113.
Studies of American Fungi. Mushrooms, Edible, Poisonous, etc.
whichbe commented on the word conchoid
A curve, of the fourth degree, first made use of by the Greek geometer, Nicomedes, who invented it for the purpose of trisecting an angle and duplicating the cube.
August 29, 2008