1926, apparently by South African Gen. J.C. Smuts (1870-1950) in his book "Holism and Evolution" which treats of evolution as a process of unification of separate parts; from Greek holos "whole" (see safe (adj.)) + -ism.
This character of "wholeness" meets us everywhere and points to something fundamental in the universe. Holism (from [holos] = whole) is the term here coined for this fundamental factor operative towards the creation of wholes in the universe. [Smuts, "Holism and Evolution," p.86]
holism ho·lism (hō'lĭz'əm)
The theory that living matter or reality is made up of organic or unified wholes that are greater than the simple sum of their parts.
A holistic investigation or system of treatment.