Noun
a word invented (usually unwittingly by subtracting an affix) on the assumption that a familiar word derives from it
Source: WordNetback formation
The existence of a Sanskrit word regularly corresponding to a Pali word is not always secure evidence of the Pali etymology, since, in some cases, artificial Sanskrit words were created by back-formation from Prakrit words. Source: Internet
The term "methyl" was derived in about 1840 by back-formation from "methylene", and was then applied to describe "methyl alcohol". Source: Internet