Geom. [ad. mod.L. subnormalis (sc. linea line): see SUB- 1 and NORMAL.] That part of the axis of abscissas which is intercepted between the ordinate and the normal at any point of the curve.
1710. J. Harris, Lex. Techn., II. s.v., This Subnormal in the Common or Apollonian Parabola, is a Determinate Invariable Quantity; for ’tis always equal to half the Parameter of the Axis.
1715. in Rigaud, Corr. Sci. Men (1841), II. 421. Because the curve AI is given, its subnormal GD will be given.
1842. Francis, Dict. Arts, s.v., In all curves the subnormal is the third proportional to the subtangent and the ordinate.
1885. Eagles, Constr. Geom. Plane Curves, 62. The focus F is found by drawing the normal at any point D, bisecting the sub-normal NG and setting off AF = 1/2 NG.
