let someone down
1. verb To cause or allow someone or something to descend. In all usages as a verb, a noun or pronoun can be used between "let" and "down." I'll let down a rope ladder for you to climb up to the treehouse. The helicopter let the rescue worker down on a harness.
2. verb To fail or disappoint someone; to neglect or be unable to do what was wanted, required, or promised to someone. Dad said he'd be here to watch my baseball game, but he let me down again. We're counting on you to close this deal, Robert—don't let down the firm.
3. verb To lower the amount of effort, attention, or focus placed on something. We'll wait long enough for them to let down their guard before we launch our invasion. After her last relationship, she found it hard to let her defenses down around men.
4. verb To lengthen a garment by extending the extra cloth in its hem. I love this dress, but it's just a bit too short. I wonder if my tailor could let it down a bit.
5. verb To make a metal slightly more ductile or malleable in the process of tempering. The blacksmith let the spear down in order to reshape it. We should let down the temper on this steel to give it a bit more flexibility.
6. noun Something that is disappointing or anticlimactic. In this usage, the phrase is often spelled with a hyphen or as a single word. Not getting tickets to the game after my aunt promised them to us is a real let down. I was really excited about my new job, but now that I've been in it for a while, it's kind of been a let-down.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
let someone down
1. Fail to support someone; also, disappoint someone. For example, I was counting on John to come, but he let me down, or The team didn't want to let down the coach. [Late 1400s] A British phrase with the same meaning is let the side down, alluding to some kind of competition (sports, politics) and dating from the mid-1900s. It is occasionally used in America.
2. let someone down easy. Convey bad or disappointing news in a considerate way, so as to spare the person's self-respect. For example, The teacher knew that Paul would have to repeat the course and that there was no way to let him down easy . [Colloquial; mid-1700s] Also see let down.
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.