The most common and most likely answer to this crossword clue is the 7 letter word LAUNDER
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More clues leading to the result LAUNDER
Buddy explains!

The straight part
We know that "Wash" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case wash = launder.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 LAUNDER mean?
LAUNDER noun- A washerwoman or washerman.
- A trough used by miners to receive powdered ore from the box where it is beaten, or for carrying water to the stamps, or other apparatus for comminuting (sorting) the ore.
- A trough or channel carrying water to the wheel of a watermill.
- A gutter (for rainwater).
- To wash; to wash, and to smooth with a flatiron or mangle; to wash and iron.
- To lave; to wet.
- (money) To disguise the source of (ill-gotten wealth) by various means.