\Di*rect"rix\, n.; pl. E. {Directrixes}, L.
{Directrices}.
1. A directress. [R.] --Jer. Taylor.
2. (Geom.)
   (a) A line along which a point in another line moves, or
       which in any way governs the motion of the point and
       determines the position of the curve generated by it;
       the line along which the generatrix moves in
       generating a surface.
   (b) A straight line so situated with respect to a conic
       section that the distance of any point of the curve
       from it has a constant ratio to the distance of the
       same point from the focus.