let one have it
v. phr.
1a. slang To hit hard.
He drew back his fist and let the man have it.
Give him a kick in the pants; let him have it!
Synonym: GIVE IT TO.
1b. slang To use a weapon on; to shoot or knife.
The guard pulled his gun and let the robber have it in the leg.
Compare: OPEN UP.
1c. or let one have it with both barrels slang To attack with words; scold; criticize.
Mary kept talking in class until the teacher became angry and let her have it.
Synonym: LIGHT INTO².
2. informal To tell about it.
■ Used in the imperative phrase, "let's have it".
Now, Mary, let's have it from the beginning.
We will take turns reading; John, let's have it from page one.

[TahlilGaran] English Idioms Dictionary ▲