The most common and most likely answer to this crossword clue is the 6 letter word LOOSEN
I've seen this crossword clue in The Times
L
O
O
S
E
N
More clues leading to the result LOOSEN
- See one’s pants go slack
- Relax, having free gin at the end
- Free toilets just north of East Newton
- Can former nurse let go?
- Relax having free gin at the end
- Convenience of having guard partially relax
- Left noose uncoiled, so relax!
- Toilet’s even unoccupied and free
- Gents perhaps needing money to relax
- Relax in rest room, soon to be empty but will be occupied by Engineer
Buddy explains!

The straight part
We know that "let go" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case let go = loosen.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 LOOSEN mean?
LOOSEN verb- To make loose.
- To become loose.
- To disengage (a device that restrains).
- To become unfastened or undone.
- To free from restraint; to set at liberty.
- To relieve (the bowels) from constipation; to promote defecation.
- To create a breach or rift between (two parties).
- To sail away (from the shore).