Springing

Spring·ing

Springing

n.
  1. The act or process of one who, or that which, springs.
  2. Growth; increase; also, that which springs up; a shoot; a plant.
    Thou blessest the springing thereof.
    — Ps. lxv. 10.

Phrases & Compounds
Springing line of an arch
the horizontal line drawn through the junction of the vertical face of the impost with the curve of the intrados; -- called also spring of an arch.