The tone of the meeting was very pessimistic.

pessimistic 是形容词，由名词 pessimism（悲观主义）加上形容词后缀 -istic 构成。pessimism 来自拉丁语 pessimus（最坏的），所以 pessimistic 表示"悲观的、消极的"，指对事情持负面预期或看法的态度。