This is the 284th most frequent Chinese word.
昨日
"昨日" means "yesterday" in English.
In this context, '昨日' is used as a noun to denote 'yesterday', a temporal reference.
昨日是一个晴朗的日子。
Yesterday was a sunny day.
Here, '昨日' metaphorically refers to 'the past' or 'times gone by'. It evokes nostalgia.
他仍旧怀念昨日的美好时光。
He still reminisces about the good times of yesterday.
'昨日' in this sentence is symbolic, representing 'previous experiences' or 'historical lessons' rather than the literal day before.