let somebody/something off phrasal verb ( see also ↑ let )
1 . to not punish someone:
I’ll let you off this time, but don’t do it again.
let somebody/something off with
After checking our identities, the customs men let us off with a warning.
let somebody off the hook (=allow someone to escape punishment or criticism)
He’d decided to make Sandra wait before letting her off the hook.
let somebody off lightly/easily (=give someone a less serious punishment than they deserve)
I think young criminals are let off far too lightly.
2 . let somebody off (something) if someone in authority lets you off something you should do, they give you permission not to do it:
You’ve worked hard all week, so I’ll let you off today.
3 . let something ↔ off to make something explode:
One boy had let off a firework in class.
⇨ let/blow off steam at ↑ steam 1 (4)