Solipsism is the idea in philosophy that the only thing you can be sure exists is your own mind. Everything else — other people, this room, the world — might be something your mind is making, and you could never prove otherwise. Very few philosophers have actually believed it; it is mostly used as a hard question that other theories of knowledge have to answer. The adjective is 'solipsistic'. In ordinary use the word has drifted, and this second use is now the more common one: calling someone solipsistic means they behave as though other people are not quite real — they never wonder how anything feels to anyone else. A film critic might say a novel is 'solipsistic' because it never looks outside the narrator's own head. That use is an insult, but a polite, educated one. It is uncountable. Take care with the pronunciation: SOL-ip-sism, and the adjective is sol-ip-SIS-tic.

唯我論（哲學上：只能確定自己的心靈存在）；引申指「只活在自己世界裡、完全不顧他人感受」