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3.
An event in which a situation turns out much better than you expected it to, in contrast to a letdown which is the exact opposite.
We were letup last night when the bleacher tickets we thought we had bought for the basketball game were actually right down by the court.
by Jobo Gusso January 21, 2011
 
1.
When you expect worse than what actually happens. A pessimist's let down. Can cause happiness and joy, or the anger and frustration brought by a let down.
I seriously expected to do worse on my test. God, what a let up!
by aslan8 December 14, 2005
 
2.
to slack off after a period of doing a reasonably acceptable job in an activity.
athletic kid: come on! only 5 more miles!

fat kid: fuck that!

athletic kid: dont let up on me now!
by domiyan November 28, 2012