undiffeˈrentiated,ppl.a. (un-1 8 and 5 b.) In very common use from c 1875. 1862H. Spencer First Princ. i. iv. §26 (1867) 96 That undifferentiated substance of consciousness which is conditioned anew in every thought.1879G. Allen Colour Sense iii. 27 Simple undifferentiated animal tissue.