Definition of mid-ordinate in US English:

mid-ordinate

noun

Mathematics
  • An ordinate erected at the midpoint of a narrow range of values of the abscissa; chiefly in "mid-ordinate rule" a method of approximating the area under a curve by dividing it into a number of vertical strips of equal width, erecting the mid-ordinate in each strip, and then multiplying the width of each strip by the sum of the mid-ordinates (which effectively takes the height of each mid-ordinate as approximating the value of the curve throughout its strip).

Origin

Late 19th century; earliest use found in Annals of Mathematics.