Sentence:  One of the best choices is the <WSD>conchoid</WSD>, according to Newton the simplest curve after the circle. 
Meaning of the word marked with <WSD> tags:  Any of a family of curves defined as the locus of points "p", such that each "p" is on a line that passes through a given fixed point "P" and intersects a given curve, "C", and the distance from "p" to the point of intersection with "C" is a specified constant (note that for nontrivial cases two such points "p" satisfy the criteria, and the resultant curve has two parts).