v. , informal 1. To become less, weaker, or quiet; become slower or stop. It's raining as hard as ever. It's not letting up at all. It snowed for three days before it let up and we could go outdoors. 2. To do less or go slower or stop; relax; stop working or working hard. Grandfather has been working all his life. When is he going to let up? Let up for a minute. You can't work hard all day. Jim ran all the way home without letting up once.
Compare: SLOW DOWN.
Antonym: BEAR DOWN. 3. To become easier, kinder, or less strict. Usually used with "on". Let up on Jane. She is sick.
Synonym: EASE UP. 4. or change up To pitch a ball at less than full speed in baseball. Usually used with "on". John pitched a ball that was very fast and the batter missed it. Then he let up on the next pitch and the batter was badly fooled.