subtangent

from The Century Dictionary.

• noun In analytical geometry, the part of the axis of abscissas of a curve cut off between the tangent and the ordinate.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Geom.) The part of the axis contained between the ordinate and tangent drawn to the same point in a curve.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun geometry The part of the axis contained between the ordinate and tangent drawn to the same point in a curve.