Dictionary.net

• sol'ip-sizm, n. the theory that self-existence is the only certainty, absolute egoism--the extreme form of subjective idealism.--n. SOL'IPSIST, one who believes in this.--adj. SOLIPSIS'TIC. [L. solus, alone, ipse, self.]

1908 - Chambers's Twentieth Century Dictionary of the English Language
By Thomas Davidson