The most common and most likely answer to this crossword clue is the 8 letter word COLONIES
I've seen this crossword clue in The Daily Telegraph
C
O
L
O
N
I
E
S
More clues leading to the result COLONIES
Buddy explains!

The straight part
We know that "settlements" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case settlements = colonies.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 COLONIES mean?
COLONIES noun- A governmental unit created on land of another country owned by colonists from a country.
- A settlement of emigrants who move to a new place, but remain culturally tied to their place of origin
- Region or governmental unit created by another country and generally ruled by another country.
- An apartment complex or neighborhood.
- A group of people with the same interests or ethnic origin concentrated in a particular geographic area
- A group of organisms of same or different species living together in close association.
- A local group of Beaver Scouts.