let down

verb

1. To disappoint; to betray or fail somebody.

   “I promised him I would meet him there, and I will not let him down.”

   “Just as they left, the younger of the two turned around and said, "Mr. President, I just want you to know that we're praying for you," and quickly closed the door behind him. I thought about these two men, and about the office workers that afternoon, and about the millions of others like them all across the country who still had faith in me. I knew that by resigning I would let them down.”

2. To lengthen by undoing and resewing a hem.
3. To reduce one's level of effort.
4. To soften in tempering.

   “to let down tools or cutlery”

5. To thin; to reduce the thickness or viscosity of.

   “let the sauce down with a little pasta water if it starts to become too thick; if the soup is too thick, you can let it down with a little milk; let the sauce down with a dash of the pickling liquor; use some of the stock to let down the onion sauce”

6. Used other than figuratively or idiomatically: see let, down: especially, to allow to descend.

   “let down your hair”

   “let down a rope”