Listening to that old song, he felt a deep saudade for his childhood days.

saudade 是葡萄牙语特有的词汇，指"对过去美好事物深切而忧郁的怀念"。这个词融合了思念、怀旧和淡淡的忧伤情绪，在英语中常直接借用，没有完全对应的词汇。