The most common and most likely answer to this crossword clue is the 6 letter word CABINS
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The straight part
We know that "shacks" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case shacks = cabins.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 CABINS mean?
CABINS noun- A small dwelling characteristic of the frontier, especially when built from logs with simple tools and not constructed by professional builders, but by those who meant to live in it.
- A chalet or lodge, especially one that can hold large groups of people.
- A private room on a ship.
- The interior of a boat, enclosed to create a small room, particularly for sleeping.
- The passenger area of an airplane.
- (travel) The section of a passenger plane having the same class of service.
- A signal box.
- A small room; an enclosed place.
- (Indian English) A private office; particularly of a doctor, businessman, lawyer, or other professional.