Definition of "yesterday" in English

noun

1. The day immediately before today; one day ago.

   • Today is the child of yesterday and the parent of tomorrow.
   • Yesterday was rainy, but by this morning it had begun to snow.

2. (figuratively) The past, often in terms of being outdated.

   • yesterday's technology
   • The worker of today is different from that of yesterday.

adverb

1. On the day before today.

   • I started to watch the video yesterday, but could only finish it this evening.

2. (informal) As soon as possible.

   • I want this done yesterday!
   • I need it yesterday!