The most common and most likely answer to this crossword clue is the 7 letter word CUPOLAS
I've seen this crossword clue in The Daily Telegraph
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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 CUPOLAS mean?
CUPOLAS noun- A dome-shaped ornamental structure located on top of a larger roof or dome.
- A small turret, usually on a hatch of an armoured fighting vehicle.
- An upward-projecting mass of plutonic rock extending from a larger batholith.
- A solid formed by joining two polygons, one (the base) with twice as many edges as the other, by an alternating band of isosceles triangles and rectangles.
- A type of furnace used for smelting.
- A small cap over a structure that is shaped like a dome or inverted cup.
- A small viewing window in the top of the caboose for looking over the train, or the part of the caboose where one looks through this window.