The most common and most likely answer to this crossword clue is the 4 letter word UNDO
I've seen this crossword clue in The Times
U
N
D
O
More clues leading to the result UNDO
- Release setter, maybe, that’s no good at all
- Some ground overlooks ruin
- Back a selection of good numbers to release
- Repeal a French act
- … and in Berlin, nothing is free
- Found out concealing key to correcting erroneous input
- Oddly missing turn, idiot has to reverse
- . Characters participating in round of Open
- Don’t start to provide money for nothing — it’s free
- Reverse effects of being bound over – to some extent
Buddy explains!

The straight part
We know that "release" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case release = undo.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does UNDO mean?
UNDO noun- An operation that reverses a previous action.
- To reverse the effects of an action.
- To unfasten.
- To impoverish or ruin, as in reputation; to cause the downfall of.