W Leibnitz (1646-1716) in his manuscript “Methodus tangentium inversa, seu  de
functionibus” written in 1673 used the word ‘function’ to mean a quantity varying
from point to point on a curve such as the coordinates of a point on the curve, the
slope of the curve, the tangent and the normal to the curve at a point However,
in his manuscript “Historia” (1714), Leibnitz used the word ‘function’ to mean
quantities that depend on a variable He was the first to use the phrase ‘function
of x’