Yesterday/ˈjestərdeɪ,ˈjestərdi/ Definition 1 of 4Pro Tip 1/2Historic Context Used to reference a very specific day in the past, not as an adjective or adverb. Yesterday was unusually warm. Pro Tip 2/2Not Recurring Refers to the most recent day before today, not to any day prior to today. She only realized it was her birthday yesterday.