n. 1. The philosophical theory that the only thing one can be sure of is the fact of one’s own existence.
2. The attitude of being extremely egocentric or self-centered.
“I think, therefore I am.” When French philosopher René Descartes wrote this, he was trying to differentiate between what he knew for certain and what he merely believed to be true. Since even his senses could sometimes deceive him, he decided that the only thing he could be absolutely, positively sure of (at least to start with) was that he existed (because he was able to think about the issue).
That is the classic example of solipsism; however, it has also come to describe, in a slightly tongue-in-cheek manner, someone who is so self-centered that they may as well be the only person in existence.
From Latin solus ‘alone’ + ipse ‘self.’
“I obviously invented solipsism.” -Dean Cavanagh