noun
Refers to a pessimistic outlook or doctrine, often used in discussions of philosophy, economics, or personal attitudes.
彼の悲観論にはうんざりだ。
I'm fed up with his pessimism.
経済の先行きについて悲観論が広がっている。
Pessimism is spreading about the economic outlook.
悲観的 is a na-adjective meaning 'pessimistic', used to describe a person's attitude or a situation, while 悲観論 is the noun for the concept or doctrine of pessimism.
Compound of 悲観 (ひかん, 'pessimistic view') + 論 (ろん, 'theory, argument').