You use yesterday to refer to the day before today. She left yesterday Yesterday she announced that she is quitting her job. Yesterday is also a noun. In yesterday's games, Switzerland beat the United States two-one
the day immediately before today; "it was in yesterday's newspapers" the recent past; "yesterday's solutions are not good enough"; "we shared many yesterdays" on the day preceding today; "yesterday the weather was beautiful" in the recent past; only a short time ago; "I was not born yesterday!