The most common and most likely answer to this crossword clue is the 11 letter word ARCHIPELAGO
I've seen this crossword clue in The Times
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More clues leading to the result ARCHIPELAGO
- Small section of block crossed by a gaoler waving a bunch of keys?
- Chap holds power over girl up in the Hebrides?
- A prig – Chloe, resolved to tour a group of islands
- Bow before cool wind getting up round islands
- Canaries perhaps shrewd changing goalie — first of penalties held
- Group at sea playing Gaelic harp with leader of orchestra
- Ship carrying computer equipment and beer going north supplying islands
- Bunch of keys?
- Islands wind up being held by corrupt rich OAP
- Geographical mix-up missing capital in Philippines?
Buddy explains!

The straight part
We know that "a group of islands" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a group of islands = archipelago.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 ARCHIPELAGO mean?
ARCHIPELAGO noun- (collective) A group of islands.
- (by extension) Something scattered around like an archipelago.