solipsistic adj.

by 1869 in translations from German of Kant's solipsismus "egoism," coined from Latin solus "alone" (see sole (adj.)) + ipse "self." The word is attested by 1817 in the German (Latin) form in English and De Quincey uses it (1827) in a footnote on Kant, but it seems not to have been picked up in English in that form.

The modern use of it, "The view or theory that self is the only object of real knowledge or the only thing really existent" [OED] seems to date to 1874 and its use in the popular translation of Ueberweg's "History of Philosophy," in reference to the implications of Schopenhauer's reasoning (and indirectly Berkeley's):

In reality there was great need, not of a proof that so-called "theoretical egoism" or "Solipsism" (the assumption by any one man that he alone exists) is a piece of lunacy, but of a proof that Schopenhauer's doctrine of the subjective nature of all categories, and his denial of their applicability to "things-in-themselves" do not logically lead to this absurd doctrine.

 "The identification of one's self with the Absolute is not generally intended, but the denial of there being really anybody else. The doctrine appears to be nothing more than a man of straw set up by metaphysicians in their reasoning." [Century Dictionary]. Earlier was soliipsiism (1826).

adjectival word-forming element, from French -istique or directly from Latin -isticus, from Greek -istikos, a compound of the adjectival suffix -ikos (see -ic) + the noun suffix -istes (see -ist).