Definition of let fall in English:

let fall

phrase

Geometry
  • Draw (a perpendicular) from an outside point to a line.

    • ‘On the tangent PR produced let fall the perpendicular SY.’
    • ‘Their effects must be estimated by the length of perpendiculars let fall upon the lines of direction in a similar manner.’
    • ‘Let ABC be any triangle, and the angle at B one of its acute angles, and upon BC, one of the sides containing it, let fall the perpendicular.’